MATERIALS  OF  CONSTRUCTION 


UNIVERSITY  OF  WISCONSIN 
EXTENSION  TEXTS 

A  series  of  Industrial  and  Engineering  Education  Textbooks, 

developed  under  the  direction  of  Dean  Louis  E.  REBER, 

University  of  Wisconsin  Extension  Division 


Norris  and  Smith's 
SHOP  ARITHMETIC 

Norris  and  Craigo's 
ADVANCED  SHOP  MATHEMA- 
TICS 

Hills' 

MACHINE  DRAWING 

George's 

ADVANCED   SHOP   DRAWING 

Wooley   and  Meredith's 
SHOP  SKETCHING 

Longfield's 

SHEET  METAL  DRAFTING 

Hobbs,  Elliott  and  Consoliver's 
GASOLINE  AUTOMOBILE 
Norris,  Winning  and  Weaver's 
GAS  ENGINE  IGNITION 

Consoliver  and  Mitchell's 
AUTOMOTIVE    IGNITION 
SYSTEMS 

Shealy's 
HEAT 

Shealy's 

STEAM  BOILERS 

Shealy's 

STEAM  ENGINES 


Jansky's 

THEORY   AND    OPERATION 
OF  D.  C.  MACHINERY 

Jansky's 

ELECTRIC  METERS 
Jansky's 

ELEMENTARY    MAGNETISM 
AND  ELECTRICITY 

Jansfy's 

PRINCIPLES  OF  RADIOTELE- 
GRAPHY 

Jansky  and  Faber's 

PRINCIPLES    OF   THE   TELE- 
PHONE 
Part    I. — Subscribers'   Apparatus 

Hool's 

ELEMENTS  OF  STRUCTURES 

Hool's 

REINFORCED    CONCRETE 
CONSTRUCTION 
Vol.   I. — Fundamental   Principles 
Vol.  II.— Retaining  Walls  and 

Buildings 
Vol.  III.— Bridges  and  Culverts 

Blair's 

SHOW  CARD  WRITING 

Pulver's 

MATERIALS    OF    CONSTRUC- 
TION 


ENGINEERING  EDUCATION  SERIES 

MATERIALS 

OF 

CONSTRUCTION 

PREPARED  FOR  THE  EXTENSION  DIVISION  OF 
THE  UNIVERSITY  OF  WISCONSIN 

BY 
H.  E.  PULVER,  B.  8.,  C.  E. 

ASSOCIATE   PROFESSOR   OF   CIVIL   AND   STRUCTURAL   ENGINEERING 
THE    UNIVERSITY    OF   WISCONSIN 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  ING. 
NEW  YORK:  370  SEVENTH  AVENUE 

LONDON:  6  &  8  BOCJVERIE  ST.,  E.  C.  4 

1922 


COPYRIGHT,  1922,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY,  INC. 


THB    MAPI-E    I'HKSS    TOKK    PA 


PREFACE 

This  textbook  has  been  prepared  for  use  in  a  correspondence- 
study  course  offered  by  the  Extension  Division  of  The  University 
of  Wisconsin.  It  is  intended  that  the  book  will  be  supplemented 
by  questions  and  problems  and  such  extra  material  as  is  found 
to  be  advisable.  The  book  is  quite  elementary  and  is  suitable 
for  students  who  have  had  an  ordinary  training  in  English  and 
Arithmetic. 

It  is  believed  that  this  text  may  also  be  of  use  for  residence 
courses  in  technical  schools,  as  the  book  is  of  such  size  that  its 
entire  contents  may  be  covered  in  the  length  of  time  usually 
assigned  to  this  subject.  The  text  should  be  used  in  connection 
with  courses  in  the  Strength  of  Materials  and  Materials  Testing 
as  no  attempt  has  been  made  to  cover  any  of  the  subject  matter 
usually  included  in  those  courses,  with  the  exception  of  a  few 
tests  and  specification  requirements. 

The  data  in  this  book  have  been  compiled  from  many  sources 
and  the  author  has  endeavored  to  give  credit  where-  it  is  due. 

The  author  is  indebted  to  Professor  D.  A.  Abrams  of  Lewis 
Institute  for  material  on  concrete  proportioning  and  to  the 
several  manufacturing  companies  and  individuals  for  illustrations 
furnished. 

H.  E.  PULVER. 
THE  UNIVERSITY  OF  WISCONSIN, 
MADISON,  WISCONSIN, 
June,  1922. 


4888-49 


CONTENTS 

PREFACE v 

CHAPTER  I.     PLASTERS  AND  NATURAL  CEMENTS 
A.  GYPSUM  PLASTERS 

ARTICLE  PAGE 

t.  Definition  and  Classification 1 

2.  Manufacture  of  Gypsum  Plasters 1 

3.  Properties  of  Gypsum  Plasters 2 

4.  Uses  of  Gypsum  Plasters 8 

B.  NATURAL  CEMENT 

5.  Definition 8 

6.  Manufacture  of  Natural  Cement 4 

7.  Properties  of  Natural  Cement  .- 4 

8.  Uses  of  Natural  Cement 6 

C.  MISCELLANEOUS  CEMENTS 

9.  Natural  Puzzolan  Cement 6 

10.  Slag  Cement .    .  6 

11.  Magnesia  or  Sorel  Cement. 7 

CHAPTER  II.     LIMES  AND  LIME  MORTARS 
A.   LIMES 

12.  Definitions  and  Classifications.    .    . 9 

13.  Manufacture  of  Quicklime 9 

14.  Manufacture  of  Hydrated  Lime 12 

15.  Manufacture  of  Hydraulic  Lime 12 

16.  Properties  of  Quicklime.    .    . 13 

17.  Properties  of  Hydrated  Lime. 14 

18.  Properties  of  Hydraulic  Lime  .    .  ... 14 

19.  Uses  of  Limes . 15 

B.  LIME    MORTARS 

20.  Lime  Mortar;  Definition  and  Materials 15 

21.  Slaking  the  Quicklime 16 

22.  Proportioning  and  Mixing  of  Lime  Mortar 17 

23.  Properties  of  Lime  Mortar 18 

24.  Common  Lime  or  Wall  Plaster 19 

25.  Uses  of  Lime  Mortar '. ' 19 

vii 


viii  CONTENTS 

CHAPTER  III.     PORTLAND  CEMENT 

A.  DEFINITION  AND  CLASSIFICATION 
ARTICLE  PAGE 

26.  Definition  of  Portland  Cement 21 

27.  Classification  of  the  Principal  Cementing  Materials 21 

B.  MANUFACTURE  OF  PORTLAND  CEMENT 

28.  Raw  Materials.    .  , 21 

29.  Proportioning  of  the  Raw  Materials 22 

30.  Outline  of  the  Dry  Process  of  Manufacture 25 

31.  The  First  Six  Steps  of  the  Dry  Process  of  Manufacture 25 

32.  The  Remaining  Six  Steps  of  the  Dry  Process  of  Manufacture   ...  29 

33.  The  Wet  Process  of  Manufacture 31 

C.   PROPERTIES  AND  USES  OF  PORTLAND  CEMENT 

34.  General 32 

35.  Chemical  Constitution  and  Specifications 32 

36.  Soundness 33 

37.  Strength 34 

38.  Time  of  Set • 35 

39.  Fineness 35 

40.  Specific  Gravity 36 

41.  Uses  of  Portland  Cement 36 

CHAPTER  IV.     PORTLAND  CEMENT  MORTARS 
A.  DEFINITIONS  AND  MATERIALS 

42.  Definitions 37 

43.  The  Cement  and  the  Water 37 

44.  Sand  in  General 37 

45.  Properties  of  Sand 38 

46.  Sieve  Analysis  of  Sand 38 

47.  Standard  Sand 39 

48.  Substitutes  for  Sand 39 

49.  Specifications  for  Fine  Aggregate 40 

B.  PROPORTIONING  AND  MIXING  MORTAR 

50.  Proportioning  the  Mortar 41 

51.  Mixing  the  Mortar.    .    . - 42 

C.  PROPERTIES  OF  PORTLAND  CEMENT  MORTARS 

52.  Strength  of  Portland  Cement  Mortars  in  General 43 

53.  Effect  of  Density  and  Size  of  Sand  on  the  Strength 43 

54.  Effect  of  the  Amount  of  Mixing  Water  on  the  Strength 44 

55.  Effect  of  Various  Conditions  on  the  Properties  of  Mortars 44 

56.  Effect  of  Various  Elements  on  the  Properties  of  Mortars 45 

57.  Tensile  Strength .46 


CONTENTS  ix 

ARTICLE  PAGE 

58.  Compressive  Strength 46 

59.  Transverse  Strength 47 

60.  Adhesive  Strength 47 

61.  Shearing  Strength 47 

62.  Miscellaneous  Properties 48 

CHAPTER  V.     PLAIN  CONCRETE 

A.  DEFINITIONS  AND  MATERIALS 

63.  Definitions 51 

64.  Cement,  Water,  and  Fine  Aggregate 51 

65.  Coarse  Aggregate  in  General 52 

66.  Size  of  Coarse  Aggregate 52 

67.  Voids,  Weight  per  Cubic  Foot,  and  Specific  Gravity  of  Coarse 

Aggregates 53 

68.  Specifications  for  Coarse  Aggregate 54 

B.  PROPORTIONING  OF  CONCRETE 

69.  General  Theory 55 

70.  Proportioning  by  Standard  Proportions 55 

71.  Proportioning  with  Reference  to  Coarse  Aggregate 56 

72.  Proportioning  with  Reference  to  Mixed  Aggregate 56 

73.  Proportioning  by  Maximum  Density  Tests 56 

74.  Proportioning  by  Mechanical  Analysis 57 

75.  Example  of  Proportioning  by  Mechanical  Analysis      ......  58 

76.  Proportioning  of  Concrete  Mixes  by  Abrams'  Method    .....  60 

77.  Proportioning  Concrete  by  Edwards'  Surface  Area  Method  ...  65 

78.  Formula  for   Estimating  Quantities  of  Materials   Required   for 

Plain  Concrete 65 

C.  MIXING  OF  CONCRETE 

79.  Hand  Mixing '. 66 

80.  Machine  Mixing 68 

81.  Consistency  of  Concrete '.>........  68 

D.  DEPOSITION  OF  CONCRETE 

82.  Forms  for  Concrete 69 

83.  Transporting,  Placing,  and  Tamping  Concrete 69 

84.  Bonding  New  Concrete  to  Old  Work 70 

85.  Surface  Finish  of  Concrete 70 

86.  Placing  Concrete  under  Water ,    .    .  71 

87.  Placing  Concrete  in  Freezing  Weather 71 

E.     IMPERVIOUS  CONCRETE 

88.  Impervious  Concrete  in  General 72 

89.  Effect  of  Increasing  the  Density  and  Amount  of  Cement   ....  72 


x  CONTENTS 

ARTICLE  PAGE 

90.  Using  Waterproofing  Materials 73 

91.  Using  Foreign  Matter  in  the  Concrete 73 

92.  Use  of  Surface  Treatments 73 

F.  PROPERTIES  OF  CONCRETE 

93.  Effect  of  Various  Impurities  Mixed  with  the  Concrete 74 

94.  Effect  of  Various  Elements  on  Hardened  Concrete 74 

95.  Effect  of  Varying  the  Amount  of  Mixing  Water 75 

96.  Strength  of  Concrete  in  General 77 

97.  Compressive  Strength  of  Concrete 78 

98.  Tensile  Strength  of  Concrete 79 

99.  Transverse  Strength  of  Concrete 79 

100.  Shearing  Strength  of  Concrete. 80 

101.  Adhesive  Strength  of  Concrete  to  Steel 80 

102.  Elastic  Limit  and  Modulus  of  Elasticity  of  Concrete 81 

103.  Yield  of  Concrete 81 

104.  Expansion  and  Contraction  of  Concrete 82 

105.  Miscellaneous  Properties  of  Concrete 82 

106.  Working  Stresses  and  Factor  of  Safety  for  Concrete 82 

107.  Rubble  Concrete 83 

G.  CONCRETE  STONE,  BLOCK,  AND  BRICK 

108.  Definitions  and  Classifications 84 

109.  Materials  for  Concrete  Stone 84 

110.  Proportions 84 

111.  Consistency 85 

112.  Mixing  and  Molding 85 

113.  Surface  Finishes 86 

114.  Curing  and  Aging 86 

115.  Properties  of  Concrete  Blocks  and  Brick 87 

116.  Uses  of  Concrete  Blocks  and  Brick 88 

CHAPTER  VI.     BUILDING  STONE 
A.  CLASSIFICATIONS  AND  DESCRIPTIONS 

117.  Building  Stone  in  General 89 

118.  Classifications  of  Building  Stone 89 

119.  Granite,  Gneiss,  and  Trap 90 

120.  Limestone,  Marble,  Sandstone,  and  Slate 91 

B.  STONE  QUARRYING  AND  CUTTING 

121.  Hand  Methods  of  Stone  Quarrying 91 

122.  Machine  Methods  of  Quarrying 93 

123.  Explosives  Used  in  Quarrying 93 

124.  Stone  Cutting 94 


CONTENTS  xi 

C.  PROPERTIES  OF  BUILDING  STONE 
ARTICLE  PAGE 

125.  Durability 96 

126.  Action  of  Frost,  Wind,  Rain,  and  Smoke 97 

127.  Action  of  Fire 98 

128.  Mechanical  Properties  of  Building  Stone 98 

CHAPTER  VII.     BRICK  AND  OTHER  CLAY  PRODUCTS 
A.  CLASSIFICATIONS  AND  DEFINITIONS 

129.  Classifications 101 

130.  Definitions 101 

B.  MANUFACTURE  OF  CLAY  BUILDING   BRICK 

131.  The  Clay 102 

132.  Hand  Process  of  Making  Brick 102 

133.  Soft  Mud  Machine  Process  of  Making  Brick 103 

134.  Stiff  Mud  Machine  Process  of  Making  Brick.    . 104 

135.  Pressed  Brick  Machine  Process  of  Making  Brick 106 

136.  Brick  Kilns 106 

137.  Burning  the  Brick 108 

C.  MANUFACTURE  OF  OTHER   BRICK 

138.  Manufacture  of  Paving  Brick ...... 108 

139.  Manufacture  of  Firebrick 109 

140.  Manufacture  of  Sand-lime  Brick Ill 

D.  OTHER  CLAY   PRODUCTS 

141.  Terra  Cotta Ill 

142.  Building  Tile   ......... ...:...  112 

143.  Drain  Tile 112 

144.  Sewer  Pipe .    .    .    , .  . 113 

E.  PROPERTIES  OF  BRICK  AND  OTHER  CLAY  PRODUCTS 

145.  General  Properties  of  Brick 114 

146.  Absorption  of  Brick  and  Building  Tile 114 

147.  Compressive  Strength  of  Brick  and  Building  Tile 115 

148.  Transverse  Strength  of  Brick  and  Building  Tile 115 

149.  Shearing  Strength  of  Brick  and  Building  Tile 116 

150.  Modulus  of  Elasticity  of  Brick  and  Building  Tile.    .......  116 

151.  Properties  of  Drain  Tile 117 

152.  Properties  of  Sewer  Pipes 118 

CHAPTER  VIII.    STONE  AND  BRICK  MASONRY 
A.  STONE    MASONRY 

153.  Stone  Masonry  in  General 119 

154.  Definitions   .  .119 


xii  CONTENTS 

ARTICLE  PAGE 

155.  Classification  of  Stone  Masonry 120 

156.  Mortar  for  Stone  Masonry 122 

157.  Dressing  of  Stone  Masonry 122 

158.  Bond  in  Stone  Masonry 122 

159.  Backing  in  Stone  Masonry 123 

160.  Pointing  of  Stone  Masonry 123 

161.  General  Rules  for  Laying  Stone  Masonry 124 

162.  Waterproofing  Stone  Masonry , 124 

163.  Cleaning  Stone  Masonry 125 

164.  Strength  and  Other  Properties  of  Stone  Masonry 125 

165.  Safe  Loads  for  Stone  Masonry 126 

B.  BRICK  AND  HOLLOW  TILE    MASONRY 

166.  Brick  Masonry  in  General 127 

167.  Mortar  for  Brick  Masonry 127 

168.  Laying  the  Brick 128 

169.  Improvements  in  Brick  Laying 128 

170.  Bond  in  Brick  Masonry 129 

171.  Pointing  of  Brick  Masonry 130 

172.  Waterproofing  Brick  Masonry 130 

173.  Cleaning  Brick  Masonry 131 

174.  Strength  and  Other  Properties  of  Brick  Masonry 131 

175.  Allowable  Working  Loads  for  Brick  Masonry 132 

176.  Efflorescence 133 

177.  Hollow  Tile  Masonry 133 

CHAPTER  IX.     TIMBER 

A.    TREES 

178.  Timber  Trees  in  General 135 

179.  Structure  of  Exogenous  Trees 135 

180.  Growth  of  Exogenous  Trees 136 

181.  Structure  and  Growth  of  Endogenous  Trees 137 

182.  Grain  and  Texture  of  Wood 138 

183.  Color  and  Odor  of  Wood 138 

184.  General  Characteristics  of  Conifers — Pine,  Fir,  and  Spruce  .    .    .  139 

185.  General  Characteristics  of  Conifers — Other  Species 140 

186.  General  Characteristics  of  Broad-leaved  Trees— Oak,  Maple,  Ash, 

Walnut 140 

187.  General  Characteristics  of  Broad-leaved  Trees — Other  Species.    .  141 

188.  General  Characteristics  of  Some  Endogenous  Trees 143 

B.  PREPARING  THE   TIMBER 

189.  Logging 143 

190.  Sawing  the  Lumber 144 

191.  Classification  of  Lumber 144 

192.  Defects  in  Lumber 145 

193.  Natural  Seasoning  of  Lumber .  147 


CONTENTS  xiii 

ARTICLE  PAGE 

194.  Artificial  Seasoning  of  Lumber 147 

195.  Shrinkage  of  Lumber 148 

C.  DURABILITY  AND  DECAY  OF  LUMBER 

196.  Durability  and  Decay  of  Lumber  in  General 149 

197.  Dry  Rot  in  Lumber 150 

198.  Wet  and  Common  Rot 151 

199.  Injurious  Insects 151 

200.  Marine  Wood  Borers 151 

D.  PROPERTIES  OF  TIMBER 

201.  Strength  of  Timber  in  General 152 

202.  Influence  of  Moisture  Content  in  Timber 153 

203.  Tensile  Strength  of  Timber '.    .    .  154 

204.  Compressive  Strength  of  Timber 154 

205.  Transverse  Strength  of  Timber 154 

206.  Shearing  Strength  of  Timber 155 

207.  Cleavability  and  Flexibility  of  Timber 155 

208.  Hardness  and  Toughness  of  Timber 156 

209.  Miscellaneous  Properties  of  Timber 156 

210.  Factors  of  Safety  and  Safe  Working  Loads  for  Timber 156 

211.  Properties  of  Timber 158 

E.  SELECTION  AND  INSPECTION  OF   TIMBER 

212.  Selection  of  Timber 158 

213.  Inspection  of  Timber 159 

F.  PRESERVATION  OF  TIMBER 

214.  Preservation  of  Timber  in  General 160 

215.  Creosote  Processes  for  Preservation  of  Timber 161 

216.  Zinc  Chloride  Pressure  Processes  for  Preservation  of  Timber   .    .  162 

217.  Vulcanizing  Process  for  Preserving  Timber 163 

218.  Some  Other  Pressure  Processes  for  Preserving  Timber 163 

CHAPTER  X.     PIG   IRON 
A.  DEFINITION  OF  PIG  IRON  AND  ORES  OF   IRON 

219.  Definition  of  Pig  Iron 165 

220.  Ores  of  Iron 165 

221.  Ore  Mining 166 

222.  Preliminary  Treatment  of  Iron  Ores 166 

B.  MANUFACTURE  OF  PIG  IRON 

223.  The  Blast  Furnace 168 

224.  Accessories  of  the  Blast  Furnace .171 


xiv  CONTENTS 

ARTICLE  PAGE 

225.  The  Fuel 171 

226.  The  Flux 172 

227.  Operation  of  the  Blast  Furnace 172 

228.  Use  of  the  Electric  Furnace  in  Reducing  Iron  Ores 174 

229.  Making  the  Pigs 175 

C.  CLASSIFICATION  AND  USES  OF  PIG  IRON 

230.  Classification  of  Pig  Iron 175 

231.  Uses  of  Pig  Iron 176 

CHAPTER  XI.     CAST  IRON 
A.  DEFINITIONS  AND  GENERAL  CLASSIFICATIONS 

232.  Definitions  of  Cast  Iron 177 

233.  General  Classification  of  Iron  and  Steel 177 

234.  Howe's  Classification  of  Iron  and  Steel 177 

B.  MAKING  THE  MOLTEN  CAST  IRON 

235.  The  Materials 178 

236.  The  Cupola 179 

237.  The  Air  Furnace 181 

C.  FOUNDRY  WORK 

238.  Definition  of  Founding 181 

239.  Patterns  and  Cores 181 

240.  Molds 182 

241.  Pouring  and  Cleaning  the  Castings 183 

242.  Defects  in  Castings 184 

D.  CONSTITUTION  AND  COMPOSITION  OF  CAST  IRON 

243.  Constitution  and  Composition  of  Cast  Iron  in  General 184 

244.  Effect  of  Carbon  in  Cast  Iron 185 

245.  Effect  of  Silicon,  Sulphur,  Phosphorus,  and  Manganese  on   Cast 

Iron 186 

246.  Effect  of  Some  Other  Chemical  Elements  on  Cast  Iron       .      .  .  188 

E.  PHYSICAL  AND  MECHANICAL  PROPERTIES  AND  USES  OF  CAST  IRON 

247.  Strength  of  Cast  Iron  in  General 188 

248.  Tensile  Strength  of  Cast  Iron 189 

249.  Compressive  Strength  of  Cast  Iron 190 

250.  Transverse  Strength  of  Cast  Iron 191 

251.  Miscellaneous  Properties  of  Cast  Iron 192 

252.  Allowable  Working  Stresses  for  Cast  Iron 192 

253.  Uses  of  Cast  Iron   .  .  192 


CONTENTS  xv 
F.  MALLEABLE  CAST  IRON 

ARTICLE  PAGE 

254.  Definition  of  Malleable  Cast  Iron 193 

255.  Making  the  Castings  for  Malleable  Cast  Iron 193 

256.  Annealing  the  Castings  for  Malleable  Cast  Iron 193 

257.  Properties  of  Malleable  Cast  Iron 194 

258.  Uses  of  Malleable  Cast  Iron V  .........  194 

CHAPTER  XII.     WROUGHT  IRON 

A.  DEFINITION  AND   CLASSIFICATIONS 

259.  Definition  of  Wrought  Iron 197 

260.  Classification  of  Wrought  Iron 197 

B.  MANUFACTURE  OF  WROUGHT  IRON 

261.  The  Materials  for  the  Wet  Puddling  Process 198 

262.  The  Furnace  Used  in  the  Wet  Puddling  Process 198 

263.  Operation  of  the  Furnace  Used  in  the  Wet  Puddling  Process   .    .  199 

264.  The  Dry  Puddling  Process 200 

265.  Mechanical  Treatment  of  the  Puddle  Balls 200 

266.  Wrought  Iron  Made  from  Scrap 201 

267.  Defects  in  Wrought  Iron 201 

C.  CONSTITUTION,  PROPERTIES,  AND  USES  OF  WROUGHT  IRON 

268.  Composition  and  Constitution  of  Wrought  Iron 201 

269.  Tensile  Strength  of  Wrought  Iron ........  202 

270.  Compressive  Strength  of  Wrought  Iron 203 

271.  Shearing  Strength  of  Wrought  Iron 203 

272.  Transverse  Strength  of  Wrought  Iron 203 

273.  Fracture  of  Wrought  Iron 203 

274.  Welding  of  Wrought  Iron 204 

275.  Miscellaneous  Properties  of  Wrought  Iron 205 

276.  Tensile  Strength  and  Ductility  Requirements  for  Wrought  Iron  .  205 

277.  Working  Stresses  for  Wrought  Iron 205 

278.  Uses  of  Wrought  Iron 206 

CHAPTER  XIII.      STEEL 
A.  DEFINITIONS  AND  CLASSIFICATIONS 

279.  Definitions  of  Steel. 207 

280.  Classifications  of  Steel  .........    .    .    .    . 207 

B.  METHODS  OF  MANUFACTURE  OF   STEEL 

281.  The  Cementation  Process 208 

282.  The  Crucible  Process. 208 

283.  The  Principle  of  the  Bessemer  Process  and  the  Plant  Equipment     .  209 

284.  The  Acid  Bessemer  Process 211 

285.  The  Basic  Bessemer  Process.                                                                .  212 


xvi  CONTENTS 

ARTICLE  PAGE 

286.  The  Principle  of  the  Open  Hearth  Process  and  the  Plant  Equipment  213 

287.  The  Acid  Open  Hearth  Process 215 

288.  The  Basic  Open  Hearth  Process 216 

289.  The  Electric  Process 217 

290.  The  Duplex  Process 218 

291.  The  Triplex  Process 218 

292.  Comparison  of  the  Different  Processes 219 

C.  COMPLETING  THE  MANUFACTURE  OF  THE  STEEL 

293.  Casting  the  Ingots 219 

294.  Defects  in  Ingots 219 

295.  Reheating  the  Ingots 220 

296.  Rolling 220 

297.  Forging  and  Pressing 221 

298.  Wire  Drawing 222 

D.  HEAT  TREATMENT  OF  STEEL 

299.  Hardening  of  Steel . 223 

300.  Tempering  of  Steel 223 

301.  Annealing  of  Steel 223 

302.  Case  Hardening  of  Steel 224 

E.  STRUCTURE  AND  CONSTITUTION  OF  STEEL 

303.  Normal  Constituents  and  Compounds 224 

304.  Critical  Temperatures 226 

305.  Slow  Cooling  of  Molten  Steel 227 

306.  Rapid  Cooling  of  Molten  Steel 227 

307.  An  Explanation  of  the  Hardening  of  Steel 228 

308.  An  Explanation  of  the  Tempering  of  Steel 228 

309.  An  Explanation  of  the  Annealing  of  Steel 229 

F.  PHYSICAL  AND  MECHANICAL  PROPERTIES  AND  USES  OF   STEEL 

310.  General 229 

311.  Effect  of  Carbon 230 

312.  Effect  of  Silicon,  Sulphur,  Phosphorus,  and  Manganese      ....  231 

313.  Effect  of  Mechanical  Working  and  Heat  Treatment 232 

314.  Tensile  Strength  of  Steel 232 

315.  Compressive  Strength  of  Steei 233 

316.  Shearing  Strength  of  Steel 234 

317.  Transverse  Strength  of  Steel 234 

318.  Average  Properties  of  Rolled  Carbon  Steels   .    .    .    .' 234 

319.  Effect  of  Combined  Stresses 235 

320.  Resistance  to  Impact  Loads 235 

321.  Ductility  of  Steel 236 

322.  Hardness  of  Steel 237 

323.  Effect  of  Repeated  and  Alternating  Stresses.    .    .  .  237 


CONTENTS  xvii 

ARTICLE  PAGE 

324.  Welding  of  Steel 238 

325.  Magnetic  Properties  of  Steel 238 

326.  Specific  Gravity  and  Coefficient  of  Expansion  of  Steel 239 

327.  Summarized  Specifications  for  Various  Steels 239 

328.  Working  Stresses  for  Structural  Steel. 240 

329.  Uses  of  Steel.    .    .'  .    .    .    .    .    .    .    ...    .    .    ...    .    .    .    .    .    .    .241 

CHAPTER  XIV.    SPECIAL  STEELS  AND  CORROSION  OF  IRON 

AND  STEEL 

A.  STEEL  CASTINGS 

330.  Definition  and  Uses  of  Steel  Castings 243 

331.  Founding  of  Steel  Castings 243 

332.  Properties  of  Steel  Castings .' 244 

B.  ALLOY  STEELS 

333.  Definition  and  Classification  of  Alloy  Steels 244 

334.  Heat  Treatment  of  Alloy  Steels 245 

335.  Nickel  Steel 246 

336.  Manganese    Steel. 246 

337.  Vanadium  Steel 247 

338.  Chrome  Steel ,    .    ." 247 

339.  Silicon  and  Aluminum  Steels 247 

340.  Tungsten,  Molybdenum,  and  Cobalt  Steels   .    .    .    . 247 

341.  Copper  Steel .....*....  248 

342.  Some  Four  and  Five  Part  Alloys 248 

C.  CORROSION  OF  IRON  AND  STEEL 

343.  Definition  of  Corrosion   ...,...,. .    .    .  249 

344.  The  Life  of  Iron  and  Steel  under  Corrosion 250 

345.  Theories  of  Corrosion 250 

346.  Prevention  of  Corrosion  in  General 251 

347.  Prevention  of  Corrosion  by  Painting 251 

348.  Prevention  of  Corrosion  by  Covering  with  Concrete  or  Asphalt    .  252 

349.  Prevention  of  Corrosion  by  Galvanizing 252 

350.  Prevention  of  Corrosion  by  Aluminum,  Nickel,  Tin,  and  Lead 

Plating 253 

351.  Prevention  of  Corrosion  by  the  Inoxidation  Process    .    .    .  ..    .    .   253 

CHAPTER   XV.     NON-FERROUS   METALS  AND   THEIR  ALLOYS 

A.  THE   NON-FERROUS   METALS 

352.  General 255 

353.  Copper .  255 

354.  Lead 256 

355.  Zinc 256 

356.  Tin.  .  257 


xviii  CONTENTS 

ARTICLE  PAGE 

357.  Aluminum 257 

358.  Nickel 258 

359.  Gold,  Silver,  amd  Platinum 258 

360.  Some  Other  Non-ferrous  Metals 259 

B.  ALLOYS  OF  NON-FERROUS  METALS 

361.  General 259 

362.  Brasses 259 

363.  Bronzes 261 

364.  Various  Aluminum  Alloys 262 

365.  Various  Nickel  Alloys 263 

366.  Bearing  Metal  Alloys 263 

367.  Fusible  Alloys 264 

368.  Solders 265 

369.  Composition  and  Use  of  Some  Miscellaneous  Alloys 265 

370.  Corrosion  of  Non-ferrous  Metals  and  Their  Alloys 265 

CHAPTER  XVI.     SOME  MISCELLANEOUS  MATERIALS 

371.  Paints,  Oils,  and  Varnishes 267 

372.  Asbestos 268 

373.  Glass 268 

374.  Glue 269 

375.  Rubber 269 

376.  Leather 271 

377.  Paper 272 

378.  Canvas 272 

379.  Ropes 272 

380.  Belts 273 

.  APPENDIXES 

A.  A.  S.  T.  M.  Standard  Specifications  and  Tests  for  Portland  Cement  275 

B.  A.    S.   T.    M.    Standard   Specifications  for     Structural     Steel     for 

Buildings 291 

C.  List  of  A.   S.  T.   M.  Standards  and  Tentative  Standards                  .  297 


MATERIALS  OF  CONSTRUCTION 

CHAPTER  I 
PLASTERS  AND  NATURAL  CEMENTS 

A.  GYPSUM  PLASTERS 

1.  Definition  and  Classification. — Gypsum  plasters  may  be 
defined  as  those  plasters  which  are  produced  by  the  partial  or 
complete  dehydration  of  gypsum.  Pure  gypsum  is  a  mixture 
of  1  part  of  calcium  sulphate  (CaSO4)  and  2  parts  of  water 
(2H20).  Gypsum  plasters  may  be  classified  as  follows: 

1.  Those  produced  by  the  incomplete  dehydration  of  the  gypsum,  the 

calcination  being  carried  on  at  a  temperature  less  than  400  degrees 
Fahrenheit, 
(a)  Plaster  of  Paris  (CaSO4  +  KH2O),  in  which  no  foreign  material 

has  been  added  either  during  or  after  the  calcination. 
(6)  Cement  plaster,  which  is  made  from  an  impure  gypsum  or    by 
adding  certain  impurities,  during  the  manufacture,  to  act  as  a 
retarder  to  the  plaster.     This  plaster  is  often  called  hard  wall  or 
patent  plaster. 

2.  Those  plasters  produced  by  the  complete  dehydration  of  the  gypsum, 

the  calcination  being  carried  on  at  temperatures  greater  than  400 
degrees  Fahrenheit. 

(a)  Calcined  plaster  (flooring  plaster),  a  pure  calcined  gypsum. 
(6)  Hard-finish  plaster,  which  is  made  by  calcining  gypsum  at  a  red 
heat  or  higher  temperature  and  to  which  certain  substances, 
such  as  alum  or  borax,  have  been  added. 

2.  Manufacture  of  Gypsum  Plasters. — The  process  of  manu- 
facture is  essentially  the  same  for  all  of  the  first  class  of  gypsum 
plasters,  variations  being  made  in  the  temperature  of  calcination 
and  the  purity  of  the  gypsum  used.  The  raw  material  is  a 
natural  gypsum  rock  usually  containing  from  1  to  6  per  cent  of 
impurities.  The  rock  is  crushed,  ground  to  a  powder,  and  then 
heated  in  a  large  calcining  kettle.  If  a  rotary  calciner  is  used, 
the  fine  grinding  is  done  after  the  calcination.  In  making  plaster 
of  Paris,  a  pure  gypsum  is  calcined  at  a  temperature  of  about 
220  degrees  Fahrenheit  thus  driving  off  three-fourths  of  the 
water  present.  Cement  plaster  is  made  in  the  same  way,  an 

1 


2  MATERIALS  OF  CONSTRUCTION 

impure  gypsum  being  used.     Often  a  retarder  (a  substance  to 
make  the  plaster  slow  setting)  is  added  after  the  calcination. 

Flooring  plaster  is  made  by  calcining  lumps  of  gypsum  in  a 
separate  feed  kiln  similar  to  the  kiln  used  for  the  calcination  of 
lime.  The  temperature  of  calcination  is  usually  about  850 
degrees  Fahrenheit  and  the  time  required  is  about  3  hours. 
Higher  temperatures  or  longer  heating  will  burn  the  plaster  and 


FIG.   1. — Rotary  cylinder  type  of  plaster  calciner. 


cause  it  to  lose  its  powers  of  setting  and  hardening.  After  the 
calcination,  the  plaster  must  be  finely  ground. 

Keene's  cement  is  the  best-known  kind  of  hard-finish  plaster. 
This  plaster  is  made  by  calcining  a  very  pure  gypsum  at  a  red 
heat,  immersing  it  in  a  10  per  cent  alum  solution,  recalcining  it, 
and  then  finely  grinding  the  calcined  material. 

3.  Properties  of  Gypsum  Plasters. — All  gypsum  plasters  will 
set  or  harden  when  mixed  with  the  proper  amount  of  water. 
The  process  is  a  combination  of  the  plaster  and  the  water  to 
form  gypsum.  The  time  required  varies  from  5  minutes  to  2 
hours  according  to  the  plaster  used  and  the  conditions  of  the 
mixing.  The  plasters  made  from  pure  gypsum  are  the  quicker 
setting  while  the  hard-burned  plasters  form  the  harder  substances. 

Very  little  data  are  available  concerning  the  strength  of 
plasters,  and  the  methods  and  conditions  of  testing  have  never 
been  standardized.  The  strength  varies  according  to  the  quality 
of  the  plaster,  the  quality  of  the  sand,  and  the  care  taken  in  the 
mixing.  The  following  table  will  give  an  idea  of  the  strength 
of  good  plasters: 


PLASTERS  AND  NATURAL  CEMENTS  3 

TENSION  TEST 

Neat  paste Age  1  month     Strength,  about  350  Ib.  per  square  inch 

1 : 2  sand  mortar Age  1  month     Strength,  about  175  Ib.  per  square  inch 

COMPRESSION  TEST 

Neat  paste Age  1  month     Strength,  1,200  to  2,000  Ib.  per  square  inch 

1 : 2  sand  mortar . .   Age  1  month     Strength,     900  to  1,500  Ib.  per  square  inch 

ADHESION  TEST 
Plaster   to    paving 

brick Age  1  month     Strength,  about  100  Ib.  per  square  inch 

Plaster  to  1 : 2  mortar.  Age  1  month     Strength,  about  130  Ib.  per  square  inch 

The  results  of  tests  have  shown  that  neat  plasters  gain  rapidly 
in  strength  for  the  first  few  days  only,  and  that  the  maximum 
tensile  and  compressive  strength  of  the  plasters  is  reached  in 
from  2  to  4  weeks.  The  mortars  gain  in  strength  a  little  less 
rapidly  than  the  neat  plasters. 

4.  Uses  of  Gypsum  Plasters. — Gypsum  plasters  are  not  used 
very  much  as  a  material  for  engineering  construction.     Plaster 
of  Paris  is  used  as  a  casting  plaster  and  for  making  quick  repairs, 
etc.,  where  a  quick  setting  plaster  is  desired.     Wall  plasters 
are  made  by  adding  lime  and  a  retarder,  together  with  hair, 
wood  fiber,  etc.,  to  a  calcined  plaster.     (Ordinary  wall  plaster 
contains  no  gypsum  plaster.)     Stucco  plaster  is  a  plaster  mixed 
with  a  dilute  solution  of  glue,  and  it  is  usually  slow  setting.     An 
addition  of  alum  or  borax  tends  to  increase  the  hardness  of  a 
plaster.     Gypsum  plasters  are  used  for  interior  wall  plasters, 
stucco  work,  architectural  ornamentation,  etc. 

Gypsum  blocks,  tile,  and  plaster  boards  are  made  from  gypsum 
wall  plaster.  These  materials  are  used  to  some  extent  in  building 
construction.  They  are  light  in  weight,  have  good  fire  resisting 
qualities,  are  strong  enough  for  many  types  of  construction, 
and  are  easily  sawn  or  cut  to  the  desired  shape.  Gypsum  wall 
plaster,  mixed  with  water  and  fine  cinders  or  wooden  chips, 
has  been  used  in  making  floors  for  buildings.  These  floors  are 
usually  lighter  in  weight  but  less  strong  and  less  fire  resistant 
than  concrete  floors. 

B.  NATURAL  CEMENT 

5.  Definition. — Natural  cement  is  the  finely  pulverized  product 
resulting  from  the  calcination  of  a  natural  argillaceous  limestone 
at  a  temperature  below  fusion.     This  temperature  should  be 
high  enough  (from  1,850  to  2,350  degrees  Fahrenheit,  to  drive 
off  the  carbon  dioxide  as  a  gas,  decompose  the  clay,  and  cause 


4  MATERIALS  OF  CONSTRUCTION 

the  formation  of  aluminates,  ferrites,  and  silicates.  The  burned 
stone  must  be  finely  ground  before  it  exhibits  any  hydraulic 
properties. 

6.  Manufacture   of  Natural   Cement. — The   rock   used   is   a 
natural  clayey  limestone  containing  from  15  to  35  per  cent  of 
clayey  material,  10  to  20  per  cent  of  the  clayey  matter  being  silica, 
and  the  balance  alumina  and  iron  oxide.     This  rock  should  occur 
in  large  deposits  and  should  be  fairly  uniform  in  composition. 

The  ordinary  form  of  kiln  in  which  the  stone  is  burned  is  a 
vertical  steel  cylinder  lined  with  firebrick  and  open  at  the  top. 
It  is  about  30  or  40  ft.  high  and  from  10  to  15  ft.  in  diameter. 

Thick  layers  of  limestone  and  thin  layers  of  soft  coal  are 
alternately  dumped  into  the  top  of  the  kiln  and  the  burned 
clinker  is  removed  through  a  door  at  the  bottom.  As  the  lime- 
stone descends  in  the  kiln  it  first  loses  its  water  and  then,  when 
a  temperature  of  about  1,400  degrees  Fahrenheit  is  reached,  the 
magnesium  carbonate  begins  to  decompose,  freeing  carbon  dioxide. 
At  a  temperature  of  about  1,650  degrees  Fahrenheit  the  carbon 
dioxide  is  driven  off  from  the  calcium  carbonate.  The  clay 
decomposes  at  a  slightly  higher  temperature  and  sets  free  alumina 
and  iron  oxide  which  combine  with  the  lime  and  magnesia  and, 
when  the  temperature  is  raised  to  about  2,200  degrees  Fahren- 
heit, form  silicates  of  lime  and  magnesia.  The  kilns  are  run 
continuously. 

If  the  stones  were  all  perfectly  burned,  the  weight  of  the  cement 
produced  would  be  equal  to  the  weight  of  the  raw  materials 
minus  that  of  the  carbon  dioxide  and  the  water  in  the  rock. 
However,  on  account  of  the  overburning  and  underburning  of 
some  of  the  rock,  about  25  per  cent  of  the  clinker  cannot  be 
used  for  cement.  The  amount  of  soft  coal  required  is  about  30 
Ib.  per  barrel  of  cement  made. 

After  the  clinker  is  removed  from  the  kiln,  it  is  allowed  to 
stand  in  air  for  a  time  so  that  any  underburned  clinker  will  be 
slaked  before  grinding.  The  slaking  may  be  hastened  by  steam- 
ing in  a  closed  vessel.  After  slaking,  the  clinker  is  crushed  in  a 
stone  crusher  and  then  ground  to  a  fine  powder  in  other  forms  of 
grinding  machinery.  Finally,  the  cement  is  packed  in  sacks  or 
barrels  for  shipment. 

7.  Properties  of  Natural  Cement. — The  chemical  composition 
of  natural  cement  is  about  as  follows:  silica,  SiO2,  20  to  30  per 
per  cent;  lime,  CaO,  30  to  60  per  cent;  magnesia,  MgO,  1  to  25 


PLASTERS  AND  NATURAL  CEMENTS 


5 


per  cent;  alumina,  A12O3,  5  to  15  per  cent;  iron  oxide,  Fe2O3, 
1  to  10  per  cent;  and  small  percentages  of  carbon  dioxide,  water, 
alkali,  and  sulphur  trioxide.  Because  of  differences  in  the 
chemical  composition  of  the  rocks  used  and  in  the  degree  of 
calcination,  the  chemical  properties  are  very  variable. 

The  specific  gravity  of  natural  cement  varies  usually  from  2.70 
to  3.10  with  an  average  of  about  2.95. 

When  mixed  with  water,  natural  cement  will  set  either  under 
water  or  in  air.  It  usually  sets  more  rapidly  than  portland 
cement.  Allowing  the  cement  to  aerate  for  some  time  will 
cause  it  to  set  less  rapidly  and  also  to  be  less  strong.  Conse- 
quently, natural  cement  should  not  be  stored  exposed  to  air 
for  more  than  a  few  weeks  before  using.  The  addition  of  gypsum 
or  plaster  of  paris  will  retard  the  set  somewhat.  The  standard 
specifications  require  initial  set  to  occur  in  not  less  than  10 
minutes  and  final  set  in  not  less  than  30  minutes  nor  more  than 
3  hours,  when  the  Vicat  needle  is  used.  The  cement  should  be 
sound,  and  test  pats  stored  in  air  and  in  water  at  normal  tem- 
perature should  remain  firm  and  hard  and  show  no  signs  of  dis- 
tortion, checking,  cracking,  or  disintegrating. 

The  cement  must  be  ground  so  fine  that  90  per  cent  of  it  will 
pass  a  standard  100-mesh  sieve  and  70  per  cent  of  it  will  pass  a 
standard  200-mesh  sieve.  In  general,  the  finer  the  cement  is 
ground,  the  stronger  it  will  be. 

Natural  cement  pastes  and  mortars  are  about  half  as  strong  as 
corresponding  portland  cement  pastes  and  mortars  in  tension, 
and  only  about  a  third  as  strong  in  compression.  When  tested 
in  compression  at  the  age  of  1  month,  neat  natural  cement  cubes 
should  average  800  Ib.  per  square  inch  or  more,  and  1:2  sand 
mortar  cubes  should  average  more  than  500  Ib.  per  square  inch. 
The  A.  S.  T.  M.  standard  specifications  for  natural  cement  require* 
that  the  tensile  strength  of  neat  natural  cement  and  1 : 3  standard 
sand  mortar  should  be  equal  to  or  more  than  the  following  values: 

TENSILE  STRENGTH 


Age  and  storage 

Neat  cement, 
pounds  per 
square  inch 

1  :  3  standard 
sand  mortar, 
pounds  per 
square  inch 

24  hours  in  moist  air   

75 

24  hours  in  moist  air,  6  days  in  water  
24  hours  in  moist  air,  27  days  in  water  

150 
250 

50 
125 

6  MATERIALS  OF  CONSTRUCTION 

8.  Uses  of  Natural  Cement. — Natural  cement  is  used  some- 
times in  structural  works  where  mass  and  weight,  rather  than 
strength,  are  required,  as  in  sewers,  conduits,  massive  founda- 
tions,  pavement  foundations,   sidewalks,    and    rarely    in    large 
masonry   dams,  abutments,  etc.     Natural  cement,  when  mixed 
with  sand    or   with   lime   and   sand,    makes  a   suitable  mortar 
for    brick  and  stone  masonry  that  is  not  subjected  to  heavy 
loads.     Natural    cement     should     not     be    used    in    exposed 
places  or  under  water  or  where  it  will  be  exposed  to  the  action 
of  frost  before  the  concrete  has  set  and  dried.     At  the  present 
time  the  use  of  natural  cement  is  decreasing,  due  to  the  decrease 
in  cost  and  the  increase  in  use  of  the  better  and  stronger  portland 
cement. 

C.  MISCELLANEOUS  CEMENTS 

9.  Natural  Puzzolan  Cement. — Natural  puzzolan   cement  is 
the  finely  pulverized  product  made  by  a  mechanical  mixture  of 
fused    argillaceous    material   and   hydrated    lime.     All   natural 
puzzolanic  materials  of  commercial  importance  are  taken  from 
the  deposits  of  volcanic  ash.     Hydrated  lime  must  be  added  to 
this  volcanic  dust  to  form  a  hydraulic  cement.     As  most  deposits 
of  puzzolana  vary  in  quality  and  fitness  for  use,  a  careful  selection 
must  be  made  at  the  quarry  to  keep  out  objectionable  materials. 
The  selected  material  is  ground  very  fine.     It  is  usually  mixed 
with  hydrated  lime  (and  also  sand)  at  the  place  where  it  is  to  be 
used  for  structural  purposes. 

Good  puzzolan  cement  mortar  of  a  1:3  mix  is  about  as  strong 
in  compression  as  a  like  mortar  made  with  portland  cement,  but 
it  is  only  about  70  per  cent  as  strong  in  tension. 
•  Natural  puzzolan  cements  were  much  used  in  the  days  of  the 
Roman  Empire  and  at  that  time  they  were  the  only  known 
cementing  materials.  At  the  present  time  these  cements  are 
used  but  very  little  in  construction  work. 

10.  Slag  Cement. — Slag  cement  is  practically  the  same  as 
puzzolan  cement  except  that  blast-furnace  slag  is  used  in  place 
of  the  puzzolan  rock.     The  slag  must  be  a  basic  slag,  such  as  is 
produced  in  the  reduction  of  iron  ores,  and  the  slag  should  be 
cooled  rapidly  when  it  is  taken  from  the  blast  furnace  so  that 
it  will  become  broken  up  into  small  pieces  which  are  easily 
handled  by  the  grinding  machinery.     The  granulation  of  the  slag 


PLASTERS   AND  NATURAL  CEMENTS  7 

tends  to  make  a  stronger  cement  and  also  to  reduce  the  amount 
of  undesirable  sulphides  present.  The  slag  is  well  dried,  finely 
ground,  and  then  thoroughly  mixed  with  the  proper  proportion 
of  hydrated  lime. 

The  specific  gravity  of  slag  cement  varies  from  2.70  to  2.85  and 
it  is  about  as  finely  ground  as  portland  cement,  though  it  is 
usually  slower  setting.  The  following  table  will  give  an  idea 
of  the  strength  of  good  slag  cement: 


STRENGTH  OF  SLAG  CEMENT 


Mix 

Age 

Tension,  pounds 
per  square  inch 

Compression  , 
pounds  per  square 
inch 

Neat  paste 

1  month 

450 

3,000 

1  :  3  sand  mortar  .  . 

1  month 

175 

700 

The  uses  of  slag  cement  are  usually  limited  to  the  unimportant 
parts  of  structural  works  which  are  not  exposed  and  which  do 
not  require  great  strength.  Slag  cement  is  used  but  very  little 
at  the  present  time. 

11.  Magnesia  or  Sorel  Cement. — This  cement  is  magnesium 
oxide,  MgO,  which,  when  mixed  with  a  proper  solution  of  mag- 
nesium chloride,  MgClo,  forms  oxychloride  of  magnesium.  This 
is  often  called  Sorel  stone  after  M.  Sorel,  a  Frenchman,  who 
was  the  first  to  note  that  this  cement  exhibited  very  strong 
hydraulic  properties.  Much  of  the  magnesium  oxide  is  obtained 
from  Greece,  though  some  is  produced  in  Canada  and  the  United 
States. 

Oxychloride  of  magnesium  is  probably  the  strongest  and 
hardest  artificial  stone  known  at  the  present  time.  Magnesia 
cement  forms  a  good,  strong,  tough  mortar  when  mixed  with 
sand,  sawdust,  asbestos,  and  other  inert  materials.  The  strength 
of  neat  pastes  and  mortars  made  with  this  cement  is  about  twice 
that  obtained  by  using  portland  cement. 

Magnesia  cement  is  used  for  floors  in  buildings  and  railway 
carriages,  for  stucco  work,  architectural  ornamentation,  etc. 
This  cement  should  not  be  used  in  water  or  where  it  will  be 
exposed  to  a  great  amount  of  moisture. 


CHAPTER  II 

LIMES  AND  LIME  MORTARS 

A.  LIMES 

12.  Definitions  and  Classifications.     1.  Quicklime. — A  white 
oxide  of  calcium,  CaO,  or  a  mixture  of  calcium  and  magnesium 
oxides,  CaO  and  MgO. 

(a)  High-calcium  lime  contains  90  per  cent  or  more  of  calcium 
oxide. 

(6)  Calcium  lime  contains  from  85  to  90  per  cent  of  calcium 
oxide. 

(c)  Magnesium    lime    contains  from   10  to  25   per   cent  of 
magnesium  oxide. 

(d)  Dolomitic  lime  contains  more  than  25  per  cent  of  mag- 
nesium oxide. 

Quicklime  may  be  divided  into  two  general  grades  as  follows: 

(a)  Selected  Lime. — A  well-burned  lime  containing  no  ashes, 

clinker,  or  other  foreign  material.     It  contains  90  per  cent  or 

more  of  calcium  and  magnesium  oxides  and  less  than  3  per  cent 

of  carbon  dioxide.     Sometimes  called  " white"  lime. 

(6)  Run-of-kiln  Lime. — A  well-burned  lime  containing  85 
per  cent  or  more  of  calcium  and  magnesium  oxides  and  less  than 
5  per  cent  of  carbon  dioxide. 

2.  Hydrated  Lime. — A  quicklime  to  which  just  enough  water 
has  been  added  to  produce  a  complete  slaking. 

3.  Hydraulic  Lime. — Obtained   from   the    calcination   of    an 
ordinary  limestone  containing  from  10  to  20  per  cent  of  clay. 

13.  Manufacture  of  Quicklime. — The  essentials  of  this  process 
are  the  heating  of  a  pure  or  magnesium  limestone  (CaCOs  or 
CaCO3  and  MgCO3)  until  the  water  in  the  stone  is  evaporated; 
then  raising  the  temperature  high  enough  for  chemical  dissocia- 
tion and  the  subsequent  driving  off  of  the  carbon  dioxide  as  a 
gas;  and  leaving  the  oxides  of  calcium  and  magnesium.     The 
maximum    temperature    required    varies    from    1,650  to  2,350 
degrees  Fahrenheit,  depending  upon  the  kind  of  limestone  and 
the  impurities  present. 

9 


10 


MATERIALS  OF  CONSTRUCTION 


The  fuels  used  in  lime  burning  are  wood,  bituminous  (soft)  coal, 
and  producer  gas.  The  soft  coal  is  not  so  good  as  wood  because 
it  burns  with  a  much  shorter  flame,  thus  causing  a  more  uneven 
heat  distribution. 

The  kilns  used  in  heating  the  limestone  are  usually  vertical 

kilns  of  the  intermittent  or  con- 
tinuous types.  Continuous  kilns 
may  be  of  the  mixed  feed, 
separate  feed,  or  ring  types. 

In  a  vertical  kiln,  the  limestone 
is  fed  in  at  the  top  end  and,  as 
it  descends,  it  first  loses  its  water 
by  evaporation;  then  the  stone 
undergoes  dissociation,  the  car- 
bon dioxide  passing  off  as  a  gas; 
and  finally  the  calcined  lime 
collects  in  the  lower  portion  of 
the  kiln,  from  which  place  it  is 
withdrawn  from  time  to  time  and 
the  underburned  and  overburned 
materials  sorted  out.  The  cooled 
lime  is  sometimes  ground  to  a 
powder  (fine  enough  to  pass  an 
80-mesh  sieve)  before  being 
placed  on  the  market. 

In  the  intermittent  or  old- 
style  form  of  kiln,  the  limestone 
is  rarely  ever  uniformly  burned 
and  the  fuel  consumption  is 
large.  Consequently,  these  kilns 
are  not  used  very  much. 

In  the  mixed-feed  type  of  kiln, 
the  mixture  of  bituminous  coal 
and  limestone  is  fed  in  at  the 
top  and  the  calcined  material 
removed  through  a  door  at  the  bottom  of  the  kiln.  Often  the 
limestone  and  fuel  are  charged  in  the  kiln  in  alternate  layers. 
The  fuel  consumption  of  this  kind  of  kiln  amounts  to  from  15 
to  25  per  cent  of  the  weight  of  the  lime  produced. 

The  vertical  kiln  with  the  separate  feed  is  made  of  steel  and 
lined  with  firebrick,  and  it  is  so  designed  that  the  limestone  does 


FIG.  2. — -Continuous  gas  fired  lime  kiln 
(Glamorgan  Pipe  &  Foundry  Co.) 


LIMES  AND  LIME  MORTARS 


11 


not  come  in  contact  with  the  fuel  during  the  burning.    The  fuel 
is  burned  in  a  grate  which  is  attached  to  the  side  of  the  kiln, 
and  so  arranged  that  the  heat  will  ascend  into  the  stack. 
Compared  with  the  separate  feed  kilns,  the  mixed  feed  kilns  are 


~-CLEVATOR    SKIP 


FIG.  3. — Mount   continuous  lime  kiln  plant.     (Glamorgan  Pipe  &  Foundry  Co.) 

cheaper  to  construct,  a  little  more  rapid  in  operation,  and  more 
economical  in  fuel,  but  they  do  not  produce  so  high  a  quality 
of  lime. 

The  ring  or  chamber  type  of  kiln  is  much  used  in  Germany. 
This  kiln  consists  of  a  series  of  chambers  grouped  around  a  central 
stack,  each  chamber  being  connected  with  the  stack  and  with 
the  other  adjacent  chambers  by  a  system  of  flues.  The  kiln 
is  charged  at  the  top  with  a  mixture  of  fuel  and  limestone.  In 


12  MATERIALS  OF  CONSTRUCTION 

the  burning,  the  flue  system  is  so  used  that  the  hot  gases  gen- 
erated in  one  chamber  will  pass  through  the  other  chambers 
before  ascending  the  stack,  thus  causing  a  preheating  of  the 
limestone  in  the  other  chambers.  This  kind  of  kiln  is  economical 
in  the  amount  of  fuel  used. 

14.  Manufacture  of  Hydrated  Lime. — The  commercial  hy- 
drated  lime  is  made  by  crushing  lump  quicklime  to  lumps  about 
half  an  inch  in  size  or  less  (some  factories  crush  the  lime  so  fine 
that  the  larger  portion  will  pass  a  50-mesh  sieve).     The  crushed 
lime  is  mixed  with  just  enough  water  to    secure    a    complete 
hydration.     This  mixing  is  usually  done  with  machinery.     The 
lumps  of  unhydrated  lime  and  other  impurities  are  removed  by 
screening  or  by  air  separation,  and  the  hydrated  lime,  in  the 
form  of  a  very  fine  powder,  is  packed  in  bags  weighing  about  100 
Ib.     For  every  56  parts  of  pure  quicklime,  18  parts  of  water  are 
required  for  the  hydration.     During  the  mixing,   considerable 
heat  is  evolved  and  the  lime  increases  in  volume.     The  final 
product  is  a  fine  powder  having  about  three  times  the  volume  of 
the  original  quicklime.     The  chemical  formula  is  Ca(OH)2. 

15.  Manufacture  of  Hydraulic  Lime. — Hydraulic  limes  include 
all  of  those  cementing  materials  (made  by  burning  siliceous  or 
argillaceous  limestones)  whose  clinker  after  calcination  contains 
so  large  a  percentage  of  lime  silicate  (with  or  without  lime  alumi- 
nates  or  ferrites)  as  to  give  hydraulic  properties  to  the  product, 
but  which  at  the  same  time  contain  normally  so  much  free  lime 
that  the  mass  of  clinker  will  slake  on  the  addition  of  water. 

The  limestone  rock  used  should  be  such  that,  after  the  silica  has 
combined  with  the  lime  during  calcination,  enough  free  lime 
remains  to  disintegrate  the  kiln  product  by  its  own  expansion 
when  it  is  slaked.  Such  a  limestone  usually  contains  from  40 
to  50  per  cent  of  lime;  about  1  per  cent  of  magnesia;  from  7  to  17 
per  cent  of  silica;  and  about  1  per  cent  of  alumina  and  iron  oxide. 

The  hydraulic  limes  are  manufactured  in  continuous  kilns  in 
the  same  way  as  quicklime  except  that  a  higher  temperature 
(never  less  than  1,850  degrees  Fahrenheit)  is  required.  After 
the  burning,  the  lumps  of  lime  are  removed  from  the  kiln  and 
slaked  in  the  same  way  as  quicklime,  great  care  being  taken  to 
use  just  the  right  amount  of  water  and  no  more,  as  an  excess 
of  water  would  cause  the  lime  to  harden.  The  expansion  of 
the  quicklime  in  slaking  breaks  up  the  lumps  into  a  fine  powder 
which  consists  principally  of  lime  silicate  with  about  25  to  33 


LIMES  AND  LIME  MORTARS  13 

per  cent  of  hydrated  lime.  The  lime  is  then  screened  through  a 
50-mesh  sieve  and  placed  in  bags. 

The  underburned  limestone  and  overburned  materials  (known 
as  grappiers),  which  are  left  after  the  hydraulic  lime  is  slaked 
and  screened,  are  ground  to  a  fine  powder  and  sold  as  "grappier" 
cement.  This  cement  is  of  value  according  to  the  proportion  of 
lime  silicate  contained  in  it. 

Lafarge  cement  is  a  hydraulic  grappier  cement  made  at  Tiel, 
France. 

16.  Properties  of  Quicklime. — Before  using,  quicklime  must 
be  slaked  by  the  addition  of  water  which  causes  the  calcium 
oxide  to  change  to  calcium  hydroxide,  Ca(OH2).  As  great  heat 
is  evolved  when  quicklime  is  slaked,  it  should  be  stored  so  that 
the  heat  caused  by  an  accidental  slaking  of  a  part  of  the  lime 
will  not  cause  a  fire.  The  rate  of  hydration  and  the  evolution 
of  heat  vary  according  to  the  purity  of  the  lime  and  the  percentage 
of  calcium,  oxide  present.  The  high-calcium  quicklimes  slake 
more  rapidly  and  generate  more  heat  than  the  other  quicklimes. 

When  the  slaked  lime  is  exposed  to  the  air,  it  gradually  absorbs 
carbon  dioxide  and  changes  from  calcium  hydroxide  to  calcium 
carbonate  (limestone)  and  water.  Dry  carbon  dioxide  will  not 
react  with  dry  hydrated  lime,  hence  an  excess  of  water  (moisture) 
must  be  present. 

On  account  of  the  large  shrinkage  in  the  hardening  of  lime 
paste,  sand  or  some  other  inert  material  must  be  added  to  reduce 
the  shrinkage  and  cracking.  The  proportions  are  usually  1 
part  of  lime  to  from  2  to  4  parts  of  sand.  The  plasticity  (quality 
of  being  spread  easily  and  smoothly  with  a  mason's  tool)  or  sand- 
carrying  capacity  of  a  lime  may  be  expressed  by  the  number  of 
parts  of  sand  which  can  be  mixed  with  1  part  of  lime  paste 
without  making  the  mortar  too  stiff  or  " short"  to  work  well 
with  a  trowel.  The  sand-carrying  capacity  of  a  lime  appears 
to  vary  with  its  purity  and  calcium  content,  the  high-calcium 
limes  being  able  to  carry  the  most  sand.  The  yield  of  a  lime  is 
the  volume  of  paste  of  a  given  consistency  produced  by  a  unit 
weight  of  dry  quicklime.  The  greater  the  purity  and  the  higher 
the  calcium  content  of  the  lime,  the  greater  the  yield.  The 
hardness  seems  to  vary  inversely,  and  the  shrinkage  to  vary 
directly,  with  the  purity  of  the  lime  and  the  percentage  of 
calcium  oxide  present. 

The  A.  S.  T.  M.  specifications  for  quicklime  in  regard  to 


14  MATERIALS  OF  CONSTRUCTION 

physical  properties  and  tests  are:  "An  average  5-lb.  sample 
shall  be  put  into  a  box  and  slaked  by  an  experienced  operator 
with  sufficient  water  to  produce  the  maximum  quantity  of  lime 
putty,  care  being  taken  to  avoid  "burning"  or  "drowning"  the 
lime.  It  shall  be  allowed  to  stand  for  24  hours  and  then  washed 
through  a  20-mesh  sieve  by  a  stream  of  water  having  a  moderate 
pressure.  No  material  shall  be  rubbed  through  the  screens. 
Not  over  3  per  cent  of  the  weight  of  the  selected  quicklime  nor 
over  5  per  cent  of  the  weight  of  the  run-of-kiln  quicklime  shall 
be  retained  on  the  sieve.  The  sample  of  lump  lime  taken  for  this 
test  shall  be  broken  to  pass  a  1-in.  screen  and  be  retained  on  a 
J^-in.  screen.  Pulverized  lime  should  be  tested  as  received." 

17.  Properties    of   Hydrated   Lime. — Hydrated    lime    is    the 
same  as  ordinary  quicklime  which  has  been  properly  slaked  and, 
therefore,  it  should  have  the  same  physical  properties.     However, 
it  has  been  observed  that  hydrated  lime  makes  a  mortar  that 
is  stronger,  more  rapid  setting,  and  which  shrinks  less  than  the 
ordinary  quicklime  mortars.     The  sand-carrying  capacity  and 
yield  of  hydrated  lime  are  usually  less  than  that  of  quicklime. 
The  better  qualities  of  the  hydrated  lime  may  be  due  to  the  more 
perfect  hydration. 

The  A.  S.  T.  M.  specifications  for  hydrated  lime  in  regard  to 
physical  properties  and  tests  are:  "A  100-gram  sample  shall 
leave  by  weight  a  residue  of  not  over  5  per  cent  on  a  standard 
100-mesh  sieve  and  not  over  0.5  per  cent  on  a  standard  30-mesh 
sieve."  "Hydrated  lime  shall  be  tested  to  determine  its  con- 
stancy of  volume  in  the  following  manner:  Equal  parts  of 
hydrated  lime  under  test  and  volume-constant  portland  cement 
shall  be  thoroughly  mixed  together  and  gaged  with  water  to 
form  a  paste.  Only  sufficient  water  shall  be  used  to  make  the 
mixture  workable.  From  this  paste  a  pat  about  3  in.  in  diameter 
and  J-2  in.  thick  at  the  center,  tapering  to  a  thin  edge,  shall  be 
made  on  a  clean  glass  plate  about  4  in.  square.  This  pat  shall 
be  allowed  to  harden  24  hours  in  moist  air  and  shall  be  without 
popping,  checking,  cracking,  warping,  or  disintegration  after  5 
hours'  exposure  to  steam  above  boiling  water  in  a  loosely  closed 
vessel." 

18.  Properties   of   Hydraulic   Lime. — Hydraulic   lime   pastes 
and  mortars  are  about  as  strong  as  those  of  natural  cement. 
Compared   with   the   values   obtained   from   tests   on   portland 
cement  pastes  and  mortars,  the  strength  of  hydraulic  lime  pastes 


LIMES  AND  LIME  MORTARS  15 

and  mortars  is  about  J£  as  strong  in  tension  and  about  y±  as 
strong  in  compression.  A  1:3  hydraulic  lime  and  sand  mortar  is 
about  70  per  cent  as  strong  as  the  neat  mix.  The  rate  of  gain 
in  strength  is  very  slow  and  the  maximum  strength  is  not  reached 
in  less  than  a  year.  Hydraulic  limes  are  about  five  times  as 
strong  in  compression  as  they  are  in  tension.  The  above  re- 
marks are  not  true  for  the  feebly  hydraulic  cements  as  those 
cements  are  very  much  weaker. 

19.  Uses  of  Limes. — About  half  of  the  lime  made  is  used  for 
various  structural  purposes,  the  remainder  being  used  for  other 
industrial  purposes  and  arts.    Most  of  the  lime  used  for  struc- 
tural purposes  is  mixed  with  sand  to  form  mortars  for  laying 
brick  and  stone  masonry.     A  large  amount  of  lime  is  used  in 
plastering  the  walls  and  ceilings  of  buildings.     Ordinary  wall 
plaster  is  a  mixture  of  lime  and  sand  to  which  hair,  fiber,  etc. 
have  been  added.     Some  lime  is  used  for  whitewashing.     A  little 
lime  is  sometimes  used  in  cement  mortars  to  make  them  more 
plastic  and  impermeable. 

Hydrated  lime  is  used  for  the  same  structural  purposes  as 
quicklime,  and  it  is  more  easily  handled,  stored,  and  shipped  as 
there  is  no  danger  of  air  slaking.  Hydrated  lime  requires  no 
slaking  before  it  is  ready  to  be  mixed  with  sand  and  water  to 
form  a  mortar.  It  is  sometimes  used  as  an  ingredient  of  portland 
cement  mortars  and  concretes. 

Hydraulic  limes  and  grappier  cements  are  sometimes  used  for 
the  purposes  of  interior  decoration.  At  one  time  they  were 
much  used  in  construction  work,  but  they  were  replaced  some 
time  ago  by  the  natural  cements,  and  later  by  portland  cement. 
Hydraulic  limes  are  not  suitable  for  use  in  underwater  work  and 
they  are  too  slow  setting  for  practical  construction  work. 

B.  LIME  MORTARS 

20.  Lime  Mortar;  Definition  and  Materials. — Lime  mortar  is 
a  mixture  of  slaked  (hydrated)  lime,  usually  in  the  form  of  a 
thick  paste,  sand,  or  other  fine  aggregate,  and  water. 

The  lime  used  is  usually  a  quicklime  which  must  be  properly 
slaked  or  hydrated  before  the  sand  or  other  fine  aggregate  is 
added.  In  general,  a  high-calcium  lime  makes  the  strongest 
and  best-working  mortar  for  ordinary  uses.  Sometimes  a 
hydrated  lime  (a  lime  which  has  been  slaked  by  the  manufacturer) 


16  MATERIALS  OF  CONSTRUCTION 

in  the  form  of  a  fine  powder  is  used.  This  hydrated  lime  requires 
no  slaking  or  other  preparation  and  is  ready  to  be  mixed  at  once 
with  the  sand  and  water  to  form  a  mortar. 

The  water  used  should  be  clean  and  contain  no  materials,  such 
as  oils,  acids,  strong  alkalis,  vegetable  matter,  etc.,  which  may 
be  injurious  to  the  mortar. 

The  sand  used  for  lime  mortar  should  be  clean  and  sharp  and 
be  composed  of  rather  small  grains  in  preference  to  large  ones. 
The  sand  should  be  free  from  all  dirt,  loam,  clay,  and  vegetable 
matter  as  these  impurities  tend  to  decrease  the  strength  and 
soundness  of  the  mortar. 

21.  Slaking  the  Quicklime. — When  quicklime  is  used,  it 
must  first  be  properly  slaked  before  being  mixed  with  the  fine 
aggregate.  It  is  important  to  secure  a  complete  slaking  of  the 
lime  and  no  more,  because,  if  too  much  water  is  added,  some  of 
the  binding  power  of  the  lime  will  be  destroyed,  and  if  too  little 
water  is  used  or  proper  care  is  not  exercised  by  the  workman,  some 
of  the  lime  may  not  be  slaked.  This  unslaked  lime  may  slake 
after  the  mortar  is  in  place  and  cause  bad  results,  especially  if 
the  mortar  is  used  as  a  wall  plaster.  If  the  quicklime  is  properly 
slaked,  the  lime  paste  formed  should  have  about  three  times  the 
volume  of  the  original  quicklime.  There  are  three  general 
methods  of  slaking  quicklime,  namely,  drowning,  sprinkling,  and 
air-slaking. 

Slaking  by  the  drowning  method  is  the  most  common  way. 
The  lumps  of  quicklime  are  placed  in  a  layer  6  or  8  in.  deep  in  a 
water-tight  box  and  then  water  is  poured  on  the  lumps.  The 
water  should  be  equal  to  about  two  and  a  half  or  three  times  the 
volume  of  the  quicklime.  If  the  proper  amount  of  water  is 
used,  the  lime  will  form  a  thick  paste.  With  a  high-calcium 
(quick-slaking)  lime,  it  is  better  to  add  the  water  all  at  once,  but 
with  a  magnesium  (slow-slaking)  lime,  the  water  should  be 
added  gradually.  As  lime  slakes  best  when  hot,  care  should  be 
taken  not  to  chill  the  lime  after  it  has  begun  to  slake.  Stirring 
may  be  necessary  to  break  up  some  of  the  lumps,  but  care  should 
be  taken  not  to  chill  the  lime  and  retard  the  slaking.  " Burning" 
occurs  when  only  a  little  water  is  present  and  this  water  is 
changed  into  steam  by  the  heat  produced.  " Burning"  tends 
to  prevent  a  complete  slaking  of  the  lime. 

Another  method  of  slaking  by  drowning  is  to  fill  a  water-tight 
box  with  about  8  in.  of  water  and  then  add  lumps  of  lime  in 


LIMES  AND  LIME  MORTARS  17 

sufficient  quantity  to  form  a  thick  paste.  The  mass  must  be 
stirred  to  assist  in  breaking  up  the  lumps  of  lime. 

Slaking  by  sprinkling  consists  of  sprinkling  a  heap  of  quicklime 
with  water  equal  to  about  one-third  or  one-fourth  of  the  volume 
of  the  lime  and  then  covering  the  mass  with  sand  and  allowing 
it  to  stand  for  a  day  or  so.  If  the  slaking  is  properly  done,  the 
hydrated  lime  will  be  in  the  form  of  a  powder.  This  method 
requires  extra  care  and  expert  labor  and  is,  consequently, 
expensive. 

Air  slaking  consists  of  spreading  the  quicklime  in  a  thin  layer 
and  allowing  it  to  slake  by  absorbing  moisture  from  the  air. 
Frequent  stirring  is  required.  This  method  produces  a  good 
quality  of  slaked  lime,  but  is  rarely  used  due  to  the  large  storage 
area,  labor,  and  time  required. 

22.  Proportioning  and  Mixing  of  Lime  Mortar. — Sand  should 
be  added  to  the  lime  paste  for  four  reasons: 

1.  To  prevent  excessive  cracking  and  shrinking  of  the  lime 
mortar  when  the  water  evaporates. 

2.  To  give  greater  strength  to  the  mortar. 

3.  To  divide  the  lime  paste  into  thin  films  and  to  make  the 
mortar  more  porous,  thus  aiding  in  the  absorption  of  carbon 
dioxide  from  the  air  which  causes  the  lime  to  set  or  harden. 

4.  To  reduce  the  cost. 

The  usual  proportions  vary  from  2  to  4  parts  of  sand  to  1  part 
of  lime  paste.  With  most  sands  and  limes,  the  correct  propor- 
tions will  be  from  2%  to  3  parts  of  sand  to  1  part  of  lime  paste 
by  volume.  Care  should  be  taken  to  secure  the  proper  propor- 
tions. The  volume  of  the  lime  paste  should  be  just  a  little  more 
than  enough  to  coat  completely  all  of  the  sand  grains  and  fill 
the  voids. 

In  mixing  the  mortar,  the  lime  paste  is  first  spread  out  in  a 
thin  layer  a  few  inches  thick  and  the  sand  spread  uniformly 
over  the  top.  The  lime  paste  and  sand  are  then  mixed  by  hoe  or 
shovel  until  the  mass  is  of  a  uniform  color.  A  little  water  should 
be  added,  if  necessary,  to  make  the  mortar  of  the  proper  con- 
sistency. Thorough  mixing  is  required  to  make  a  good  mortar. 

When  hydrated  lime  in  the  form  of  a  powder  is  used,  the  lime 
and  sand  should  be  mixed  dry  until  of  a  uniform  color  and  then 
sufficient  water  should  be  added  and  the  whole  mixed  until  the 
mortar  is  of  the  proper  consistency. 

If  too  much  sand  has  been  used  the  mortar  will  be  "short" 
2 


18  MATERIALS  OF  CONSTRUCTION 

and  "stiff"  and  will  not  work  properly;  while  if  too  much  lime 
paste  is  used,  the  mortar  will  be  too  sticky  to  work  properly. 
A  mason  can  tell  very  quickly  whether  the  mortar  is  correctly 
proportioned  or  not  when  he  starts  to  use  the  mortar  in  his 
work.  The  proportions  which  give  the  best  working  mortar  are 
also  the  best  proportions  in  regard  to  strength,  hardening, 
and  other  properties  (except  when  clay  or  loam  is  used  instead 
of  sand). 

About  210  Ib.  of  good  quicklime  are  required  to  make  a  cubic 
yard  of  1 : 3  lime  mortar. 

23.  Properties  of  Lime  Mortar. — Lime  mortar  has  the  import- 
ant property  of  " setting"  or  " hardening"  when  the  water 
evaporates  and  the  lime  absorbs  carbon  dioxide  from  the  air 
thus  forming  calcium  carbonate.  This  setting  takes  place  very 
slowly,  especially  if  the  mortar  is  placed  in  thick  layers  or  in 
places  where  it  is  difficult  for  the  air  to  reach,  and  sometimes 
many  years  are  required  for  the  hydrated  lime  to  change  to 
calcium  carbonate. 

In  a  lime  mortar,  an  excess  of  lime  paste  delays  the  hardening, 
increases  the  shrinkage,  decreases  the  compressive  strength, 
and  makes  the  mortar  sticky.  An  excess  of  sand  makes  the 
mortar  " short"  and  hard  to  work  with  a  mason's  tools  besides 
decreasing  the  strength  of  the  mortar. 

The  freezing  of  lime  mortar  delays  the  evaporation  of  the  water 
and  thus  delays  the  absorption  of  carbon  dioxide  from  the  air. 
The  expansion  of  the  water  due  to  the  freezing  may  damage  the 
mortar.  Alternate  freezing  and  thawing  decrease  the  adhesive 
and  cohesive  strength. 

A  fine,  sharp,  clean  sand  gives  the  best  results  in  a  lime  mortar. 

Clay,  loam,  dirt,  etc.  decrease  the  strength  of  lime  mortar, 
hence  these  materials  should  not  be  used. 

Oils,  acids,  strong  alkalis,  vegetable  matter,  etc.  decrease  the 
strength  and  hardening  qualities  of  a  lime  mortar. 

The  tensile  strength  of  a  good  1 : 3  lime  mortar,  1  month  old, 
varies  from  30  to  60  Ib.  per  square  inch.  When  it  is  6  months 
old,  the  strength  will  probably  be  from  10  to  15  Ib.  more  per 
square  inch. 

The  compressive  strength  of  a  good  1 : 3  lime  mortar,  at  the 
age  of  1  month,  will  probably  be  between  150  and  400  Ib. 
per  square  inch.,  while  at  the  age  of  6  months  the  strength  may 
vary  from  17Q  to  750  Ib.  per  square  inch.  The  strength  of  a  lime 


LIMES  AND  LIME  MORTARS  19 

mortar  depends  upon  the  quality  of  the  lime  and  the  sand  and 
upon  the  care  taken  during  the  mixing,  molding,  storing,  and 
testing. 

A  magnesium  lime  mortar  is  usually  stronger  and  quicker 
setting  than  a  high-calcium  lime  mortar. 

24.  Common  Lime  or  Wall  Plaster. — Common  lime  or  wall 
plaster  is  a  lime  sand  mortar  in  which  hair,  fiber,  or  some  similar 
material  has  been  thoroughly  mixed.     The  hair  or  fiber  is  added 
to  keep  the  plaster  from  shrinking  and  cracking  when  it  sets  and 
hardens  on  the  wall. 

Wall  plaster  is  usually  applied  in  two  coats.  The  first  or  rough 
coat  is  put  on  about  half  an  inch  thick.  It  consists  of  about  a 
1 : 3  lime  mortar  to  which  the  fiber,  etc.  have  been  added.  The 
exposed  surface  is  troweled  smooth,  but  no  effort  is  taken 
to  make  a  very  smooth  surface. 

The  second  or  finishing  coat  is  added  after  the  first  coat  has 
dried.  This  finishing  coat  consists  of  a  rich  mortar  (a  1 : 1  or 
1 : 2  mix)  made  of  a  very  white  lime  paste  and  a  fine,  sharp,  clean, 
light-colored  sand.  This  coat  is  applied  in  a  very  thin  layer  and 
care  is  taken  to  secure  a  very  smooth-finished  surface. 

It  is  important  that  the  quicklime  used  in  a  wall  plaster 
shall  be  thoroughly  slaked  before  it  is  placed  on  the  wall.  This 
is  usually  made  sure  of  by  allowing  the  plaster  to  remain  in  a 
water-tight  box  for  several  days  before  it  is .  applied  to  the  • 
wall.  If  any  unslaked  lime  is  placed  in  the  wall,  it  will  absorb 
moisture,  slake,  expand,  and  form  "blisters"  on  the  wall  surface, 
often  injuring  the  wall  so  much  that  the  plastering  has  to  be 
done  over  again. 

A  ''whitewash"  is  a  thin  paste  made  of  white  quicklime  and 
water  which  is  applied  to  the  wall  or  other  surface  by  means  of 
a  brush.  As  many  coats  as  desired  may  be  applied.  A  "white- 
wash" serves  the  same  purpose  as  a  cheap  paint. 

25.  Uses  of  Lime  Mortar. — Lime  mortar  is  used  as  a  mortar 
for  stone  and  brick  masonry,  where  the  mortar  can  be  placed  in 
comparatively  thin  layers  and  the  walls  are  not  very  thick, 
and  where  great  strength  is  not  required.     Lime  mortar  should 
not  be  used  in  massive  masonry,  under  water,  or  in  a  wet  soil, 
as  the  lime  will  not  harden  unless  it  can  absorb  carbon  dioxide 
from  the  air. 

In  places  where  great  strength  is  required,  a  portland  cement 
mortar  should  be  used. 


20  MATERIALS  OF  CONSTRUCTION 

Lime  mortar  is  sometimes  mixed  with  portland  cement  mortar 
to  make  the  portland  cement  mortar  easier  to  work  and  also 
where  a  mortar  stronger  than  lime  mortar  is  required. 

Lime  mortar  is  much  used  as  a  wall  plaster  and  for  stucco 
work,  etc. 


CHAPTER  III 

PORTLAND  CEMENT 

*        A.  DEFINITION  AND  CLASSIFICATION 

26.  Definition  of  Portland  Cement.— Portland  cement  is  the 
product   obtained   by   finely   pulverizing   clinker   produced  by 
calcining  to  incipient  fusion,  an  intimate  and  properly  propor- 
tioned mixture  of  argillaceous  and  calcareous  materials,  with  no 
additions  subsequent  to  calcination  excepting  water  and  calcined 
or  uncalcined  gypsum  (Am.  Soc.  Test.  Mat.). 

27.  Classification  of  the  Principal  Cementing    Materials. — 
At  the  present  time  the  knowledge  of  cement  chemistry  is  not 
complete  enough  to  allow  of  the  classification  of  cementing  materials 
according  to  their  chemical  properties.     However,  the  different 
kinds  of  cementing  materials  may  be  classified  according  to  their 
methods  of  manufacture  and  physical  properties.     The  following 
classification  brings  out  the  main  differences  in  the  manufacturing 
methods  and  the  slaking  and  hydraulic  properties  of  the  five 
main-cementing  materials. 

1.  Common  Lime. — Made  by  burning  relatively  pure  limestone  at  a  very 
low  temperature.     It  will  slake  when  mixed  with  water  and  it  has  no  hy- 
draulic properties. 

2.  Hydraulic  Lime. — Made  by  burning  slightly  argillaceous  limestone  at 
a  low  temperature.     It  will  slake  slowly  and  has  feebly  hydraulic  properties. 

3.  Natural  Cement. — Made  by  burning  argillaceous  limestone  at  a  com- 
paratively high  temperature.     It  will  not  slake  but  it  has  hydraulic  proper- 
ties when  ground. 

4.  Portland     Cement. — Made    by    burning    an    artificial    mixture    of 
argillaceous  and  calcareous  materials  to  a  temperature  of  incipient  fusion. 
It  will  not  slake  but  it  has  very  marked  hydraulic  properties  when  finely 
ground. 

5.  Puzzolan  or  Slag  Cement. — Made  by  mixing  slaked  lime  with  granu- 
lated blast-furnace  slag  or  a  natural  puzzolanic  material.     It  will  not  slake 
but  possesses  hydraulic  properties  when  ground. 

B.  MANUFACTURE  OF  PORTLAND  CEMENT 

28.  Raw  Materials. — A  large  number  of  materials  are  available 
for  use  in  the  manufacture  of  Portland  cement.     The  following 

21 


22  MATERIALS  OF  CONSTRUCTION 

are  the  materials  most  commonly  used  and  they  are  arranged 
about  in  the  order  of  their  importance. 

ARGILLACEOUS  CALCAREOUS 

MATERIALS  MATERIALS 

Argillaceous  limestone  (cement  and  pure  limestone 

rock) 

Clay  or  shale  and  pure  limestone 

Clay  or  shale  and  marl 

Blast-furnace  slag  and  pure  limestone 

Clay  or  shale  and  chalk  or  chalky  limestone 

Clav  or  shale  and  alkali  waste 

Cement  rock  is  a  soft,  impure,  argillaceous  limestone  containing 
about  20  per  cent  of  clay  and  70  per  cent  of  calcium  carbonate. 

Limestone  suitable  for  cement  manufacture  consists  principally 
of  calcium  carbonate  (90  per  cent  or  more)  with  small  percentages 
of  silica,  aluminium  and  iron  oxides,  magnesium  carbonate, 
sulphur,  and  various  alkalis. 

Marl  is  a  deposit  of  soft  and  comparatively  pure  limestone 
usually  found  in  the  beds  of  extinct  and  existing  lakes. 

Shales  are  a  soft  rock  composed  chiefly  of  silica,  alumina,  and 
iron  oxide. 

Clays  result  from  decayed  shales  and,  consequently,  have  about 
the  same  chemical  composition  with  a  little  more  water. 

Slate  is  a  form  of  shale. 

Blast-furnace  slag  is  a  fusible  silicate  formed  during  the  reduc- 
tion of  the  iron  ore  in  a  blast  furnace  by  the  combination  of  the 
fluxing  material  (limestone,  etc.)  with  the  earthy  matter  (gangue) 
of  the  ore. 

Chalk  is  a  soft  variety  of  calcium  carbonate  formed  from  the 
remains  of  minute  organisms.  It  also  contains  small  percentages 
of  silica,  alumina,  and  magnesia. 

Alkali  waste  is  the  precipitated  calcium  carbonate  obtained 
during  the  manufacture  of  caustic  soda  by  the  Leblanc  process. 

In  order  to  secure  the  proper  chemical  combinations  in  the 
kiln,  all  of  the  calcareous  materials  should  be  free  from  quartz  or 
sand  and  should  contain  but  little  sulphur  or  magnesium  car- 
bonate. The  clays  should  also  be  free  from  sand  and  harmful 
impurities.  Soft  limestones  are  more  easily  ground  than  hard 
ones. 

29.  Proportioning  of  the  Raw  Materials. — Portland  cement 
has  a  complex  chemical  composition  consisting  for  the  most  part 
of  tricalcium  silicate  (3CaOSiO2),  dicalcium  silicate  (2CaOSi02), 


PORTLAND  CEMENT 


23 


and  tricalcium  aluminate  (SCaOA^Oa),  with  small  amounts  of 
other  compounds,  resulting  from  the  burning  of  the  calcium  car- 
bonates, silicates,  and  alumina.  Hence,  the  proportions  of 
argillaceous  and  calcareous  materials  must  be  carefully  chosen 
in  order  to  secure  the  proper  results.  Eckel's  formula  for  the 
correct  theoretical  proportions  for  Portland  cement  is: 

2.8  Silica  (SiO2)  + 1. 1  Alumina  ( A12O3)  +0.7  Iron  Oxide  (Fe2O3)  = 
1.0  Lime  (CaO)  +  1.4  Magnesia  (MgO) 

An  average  portland  cement  contains  about  22.0  per  cent  of 


FIG.  4.— Flow  sheet  for  a  dry  process  Portland  cement  plant.      (Allis-Chalmers 

Mfg.  Co.) 

silica,  7.4  per  cent  alumina,  3.0  per  cent  iron  oxide,  62.0  per  cent 
lime,  1.75  per  cent  magnesium  oxide,  1.3  per  cent  of  sulphuric 
acid,  and  about  1.0  per  cent  of  alkalis. 


24 


MATERIALS  OF  CONSTRUCTION 


An  excess  of  lime  makes  the  cement  unsound,  while  too  little 
lime  causes  the  cement  to  be  quick  setting  and  weak.  In  order 
to  avoid  an  excess,  the  lime  content  is  kept  a  little  below  the 
value  given  by  the  formula. 

SLAG  CoAL 


FIG.  5. — Flow  sheet  for  a  thousand  barrel  dry  process  slag  Portland  cement 
plant.      (Allis-Chalmers  Mfg.   Co.) 

The  amount  of  alumina  present  has  a  large  effect  on  the  clinker- 
ing  temperature,  the  more  the  alumina  the  lower  the  temperature 
required.  Large  amounts  of  alumina  tend  to  make  the  cement 
quick  setting  and  weak  as  well  as  to  render  the  cement  more 
liable  to  disintegration  when  exposed  to  the  action  of  sea  water. 


PORTLAND  CEMENT  25 

Magnesia,  up  to  4  or  5  per  cent,  appears  to  have  no  bad  effect 
on  the  cement,  but  larger  amounts  are  thought  to  be  injurious. 

Calcium  sulphate,  as  gypsum  or  plaster  of  Paris,  is  added  to 
the  cement  after  burning  to  retard  the  set.  The  amount  is 
usually  less  than  three  per  cent. 

Sulphuric  acid  (SO3)  is  limited  to  200  per  cent  by  the  specifica- 
tions. 

30.  Outline  of  the  Dry  Process  of  Manufacture. — The  dry 
process  of  manufacture  of  Portland  cement,  which  is  the  most 
important  process  of  manufacture,  consists  of  the  following  steps 
(though  not  always  in  the  exact  order  as  given) : 

1.  Securing  the  raw  materials. 

2.  Crushing  the  raw  materials. 

3.  Drying  the  raw  materials. 

4.  Grinding  the  raw  materials.1 

5.  Proportioning  and  mixing. 

6.  Finely  grinding  the  materials.1 

7.  Burning  the  materials. 

8.  Cooling  the  clinker. 

9.  Addition  of  the  retarder. 

10.  Grinding  clinker  to  a  very  fine  powder. 

11.  Seasoning  the  cement. 

12.  Packing  the  cement  for  shipment. 

31.  The  First  Six  Steps  of  the  Dry  Process  of  Manufacture.— 
1.  Most  of  the  raw  materials  are  obtained  by  quarrying,  after 
which  they  are  transported  to  the  factory.     Blasting  is  required 
for   the   harder  materials,  while  the  softer  materials  may  be 
excavated  with  a  steam  shovel.     Marl  is  often  dredged.     Blast- 
furnace slag  is  secured  from  the  blast  furnace. 

2.  Nearly  all  of  the  raw  materials  need  to  be  crushed  to  smaller 
sizes  before  they  can  be  handled  by  the  grinders.     The  crushing 
is  done  by  means  of  jaw,  roller,  or  gyratory  crushers  and  often 
both  large  and  small  crushers  are  used  to  make  the  materials  fine 
enough  for  the  grinders.     The  gyratory  type  of  crusher  is  used 
more  than  the  other  types  because  it  is  more  economical  in 
operation.     The  raw  materials  are  usually  crushed  so  that  they 
will  pass  through  a  2-in.  ring. 

3.  The  drying  is  usually  done  in  a  revolving,  hollow,  steel 
cylinder  about  5  ft.  in  diameter  and  50  ft.  long  and  which  is 
inclined  a  little  to  the  horizontal.     The  materials  enter  at  the 
upper  end  and  pass  out  of  the  lower  end.     The  dryer  removes  the 
water  from  the  materials. 

1  NOTE. — In  the  newer  types  of  cement  mills,  both  the  coarse  and  fine 
grinding  (processes  4  and  6)  are  done  in  one  mill. 


26 


MATERIALS  OF  CONSTRUCTION 


4.  The  preliminary  grinding  is  often  done  in  a  ball  mill  which  is 
a  short,  closed,  hollow  cylinder  that  revolves  about  its  longitud- 


FIG.  6. — Jaw  crusher.     (Allis-Chalmers  Mfg.  Co.) 


FIG.  7. — Gyratory  crusher.     (Allis-Chalmers  Mfg.   Co.) 

inal  axis.  The  grinding  is  done  by  a  number  of  hard  steel  balls, 
from  3  to  5  in.  in  diameter,  placed  in  the  cylinder.  The  materials 
are  ground  so  that  they  will  pass  a  20-mesh  sieve.1 

1  NOTE. — In  the  later  type  of  cement  plants,  both  the  coarse  and  fine 
grinding  are  done  in  one  mill,  called  a  compeb  mill.  This  mill  is  divided 
into  two  parts.  The  coarse  grinding  is  done  in  the  first  part,  after  which 
the  material  passes  into  the  second  part  for  the  fine  grinding.  The  use  of 
this  type  of  mill  eliminates  process  4  (grinding  the  raw  materials). 


PORTLAND  CEMENT 


27 


FIQ.  8.— Direct  heat  rotary  dryer.     (Allis-Chalmers  Mfg.  Co.) 


CXM^W 


ffg.  Co.) 


FIG.  10. — Coropeb  mill.     (Allis-Chalmers  Mfg.  Co.) 


28 


MATERIALS  OF  CONSTRUCTION 


5.  The  materials  then  pass  through  a  weighing  machine  where 
they  are  weighed  out  in  the  correct  proportions  and  then  dumped 
in  a  mixing  hopper  where  they  are  thoroughly  mixed  together. 


FIG.   11. — Compeb  mill  section.      (Allis-Chalmers  Mfg.   Co.) 


6.  From  the  mixing  hopper,  the  materials  pass  into  a  mill  (such 
as  a  tube,  Gates,  Fuller-Lehigh,  or  Griffin  mill,  etc.)  for  a  finer 
grinding.  The  tube  mill,  which  is  more  often  used  than  any 


FIG.  12.— Gates  tube  mill.     (Allis-Chalmers  Mfg.  Co.) 

other,  is  a  closed  steel  cylinder  about  5  ft.  in  diameter  and  22  ft. 
long  which  is  lined  with  a  material  (that  has  a  high  abrasive 
resistance)  such  as  chilled  cast  iron  or  trap  rock.  The  grinding 
is  done  by  a  number  of  flint  rocks,  about  the  size  of  goose  eggs, 


PORTLAND  CEMENT 


29 


which  fill  the  mill  about  half  full.  The  materials  are  ground  so 
fine  that  about  95  per  cent  of  the  powder  will  pass  a  100-mesh 
sieve.  (See  footnote,  page  25.) 


FIG.  13. — Fuller-Lehigh    mill.     (Fuller-Lehigh    Co.) 

32.  The  Remaining  Six  Steps  of  the  Dry  Process  of  Manufac- 
ture.— 7.  The  finely  ground  material  from  the  tube  mills  passes 
into  the  upper  end  of  a  rotary  type  of  cement  kiln  where  it  is 
burned.  The  rotary  kiln  is  a  long  steel  cylinder,  6  to  9  ft.  in 
diameter  and  from  100  to  150  ft.  in  length,  which  is  slightly 
inclined  to  the  horizontal  and  is  so  made  that  it  can  be  slowly 


30  MATERIALS  OF  CONSTRUCTION 

rotated.  The  fuel  used  is  a  finely  powdered  coal  which  is  blown 
through  a  nozzle  inserted  in  the  lower  end  of  the  kiln.  A  brick 
flue,  leading  to  a  smokestack,  is  attached  to  the  upper  end  of  the 
kiln.  Soon  after  the  material  enters  the  upper  end  of  the  kiln 
it  balls  up  in  small  balls  and,  as  it  moves  slowly  down  the  kiln, 
the  water  is  evaporated  and  the  most  of  the  carbon  dioxide  is 
driven  off.  As  the  material  approaches  the  lower  end  of  the 
kiln,  all  of  the  carbon  dioxide,  sulphur,  and  organic  matter  is 
expelled.  A  few  feet  from  the  lower  end  the  temperature  reaches 
2,900  to  3,100  degrees  Fahrenheit  and  the  little  brown  balls  are 


FIG.  14. — Rotary  kiln  with  taper  end.     (Allis-Chalmers  Mfg.   Co.) 

fused  into  a  hard  dark-colored  clinker.     The  time  required  for 
the  passage  of  the  material  through  the  kiln  is  four  or  five  hours. 

8.  After  the  burning,  the  clinker  is  removed  from  the  kiln  and 
sprayed  with  a  stream  of  water.     Then  the  clinker  is  passed 
through  a  cooler  and  placed  in  the  clinker  storage  bins. 

9.  When  the  clinker  is  removed  from  the  clinker  storage  bins, 
it  passes  through  a  weighing  machine  where  the  retarder  is  added. 
The  reason  that  something  is  added  to  retard  the  set  of  the  cement 
is  that  the  high-lime  content  would  make  the  cement  too  quick 
setting  for  commercial  use.     The  quantity  added  is  about  2  per 
cent,  usually,  and    never   more  than  3  per  cent.     Gypsum  is 
usually  used  as  a  retarder  though  plaster  of  Paris  is  sometimes 
used. 

10.  After  the  retarder  is  added  the  clinker  is  ground  to  a  very 
fine  powder  in  a  mill  similar  to  the  one  used  for  finely  grinding  the 
material  before  burning.     The  clinker  must  be  ground  so  fine 
that  78  per  cent  or  more  will  pass  a  standard  200- mesh  sieve. 


PORTLAND  CEMENT 


31 


11.  After  the  final  grinding,  the  cement  is  conveyed  to  a 
storage  bin  and  allowed  to  season  for  a  few  weeks  before  being 
packed  for  shipment.  These  storage  bins  usually  have  a  capacity 
varying  from  1,000  to  5,000  bbl.  each.  The  seasoning  seems  to 
improve  the  quality  of  the  cement. 


FIG.   15. — Flow  sheet  for  a  wet  process  Portland  cement  plant. 

Mfg.  Co.) 


(Allis-Chalmers 


12.  For  shipment,  the  cement  is  packed  in  bags  or  sacks  holding 
about  94  Ib.  of  cement,  or  in  barrels  which  hold  the  equivalent  of 
four  sacks  or  376  Ib.  of  cement.  Sometimes  the  cement  is  placed 
in  bulk  in  a  railroad  car  and  so  shipped. 

33.  The  Wet  Process  of  Manufacture. — The  raw  materials 
most  commonly  used  in  this  process  are  clay  and  chalk  or  marl. 


32  MATERIALS  OF  CONSTRUCTION 

The  clay  is  dried  and  then  ground  in  an  edge  runner  mill,  while 
the  other  materials  are  ground  in  a  wash  mill  where  enough  water 
is  used  to  make  them  into  a  thin  mud  or  slurry.  Then  the 
proper  quantities  of  the  materials  are  weighed  out  and  mixed  in  a 
pug  mill,  the  slurry  pumped  into  a  large  vat,  a  chemical  analysis 
made,  and  more  materials  added  if  necessary.  The  slurry  is  then 
pumped  from  the  vat  to  a  special  rotary  kiln  in  which  it  is  burned. 
After  the  clinker  is  removed  from  this  kiln,  the  process  of  manu- 
facture is  the  same  as  that  of  the  dry  process. 

The  wet  process  of  manufacture  allows  of  better  chemical  con- 
trol and  easier  grinding,  but  it  requires  more  fuel  for  the  burning. 
Because  of  this  the  dry  process  is  usually  cheaper  and,  conse- 
quently, more  often  used. 

C.  PROPERTIES  AND  USES  OF  PORTLAND  CEMENT 

34.  General. — Cement  is  valuable  as  a    structural    material 
because  it  has  mechanical  strength  after  hardening.     In   order 
to  compare  the  mechanical  strengths  of  different  cements  and 
their  fitness  for  structural  work,  it  is  necessary  to  make  stand- 
ardized tests  and  laboratory  experiments  on  some  of  the  physical 
and  mechanical  properties.     These  qualities  in  the  order  of  their 
importance  are:  soundness,  strength,  time  of  set,  fineness,  and 
specific  gravity.     The  determinations  of  some  of  the  chemical 
properties  by  standardized  chemical  tests  aid  in  deciding  whether 
a  cement  is  suitable  or  not  for  structural  purposes. 

35.  Chemical    Constitution    and    Specifications. — The    latest 
studies  on  the  chemical  constitution  of  Portland  cement  seem  to 
indicate    that    portland    cement    is   made   up   largely    of  three 
compounds,  namely:  tricalcium  silicate   (3CaOSi02),  dicalcium 
silicate    (2CaOSiO2),    and   tricalcium   aluminate    (3CaOAl2O3). 
There   are  also  small  amounts  of  iron  oxide  (Fe2O3),  magnesia 
(MgO),  sulphur  in  the  form  of  SO3,  alkalis,  etc.,  together  with  a 
little    lime   (CaO)   if  the  clinker  is  underburned.     A  perfectly 
burned  cement  clinker   consists  of  about  36  per  cent  of  trical- 
cium   silicate,    33    per   cent   of  dicalcium  silicate,  21  per  cent 
of  tricalcium  aluminate,  and  about  10  per  cent  of  other  com- 
pounds.    If  the  cement  clinker  is  not  perfectly  burned,  there  is 
less  tricalcium  silicate  and  more  dicalcium  silicate  and  usually 
some  free  lime. 

The  standard  specifications  for  Portland  cement  specify  that, 


PORTLAND  CEMENT  33 

in  regard  to  chemical  properties,  the  following  limits  shall  not 
be  exceeded: 

Loss  on  ignition 4 . 00  per  cent 

Insoluble  residue 0 . 85  per  cent 

Sulphuric  anhydride  (SO3) .    2.00  per  cent 

Magnesia  (MgO) 5 . 00  per  cent 

36.  Soundness. — Soundness  is  a  necessary  quality  for  cement 
that  is  to  be  used  for  structural  purposes,  as  it  is  not  desirable 
to  use  a  cement  that  will  later  disintegrate  and  cause  a  failure 
of  the  structure.  Unsoundness  is  usually  shown  by  expansion 
after  the  cement  has  set,  followed  by  disintegration.  Free 
lime  is  the  chief  cause  of  unsoundness,  causing  the  cement  to  ex- 
pand and  disintegrate.  An  excess  of  magnesia  (more  than  5  per 
cent)  is  thought  to  cause  unsoundness.  An  excess  of  sulphate 
is  thought  to  have  a  similar  action  in  some  cases.  Seasoning 
helps  in  making  cement  sound  by  giving  time  for  the  complete 
hydration  or  carbonating  of  any  free  lime  that  is  present.  Un- 
soundness is  shown  by  the  cracking  and  disintegration  of  the 
cement  after  setting,  due  to  the  expansion  of  some  of  its 
constituents.  The  amount  of  sulphates  added  for  a  retarder 
should  never  be  more  than  3  per  cent.  Soundness  is  promoted 
by  thorough  seasoning,  fine  grinding,  and  by  keeping  the  amounts 
of  magnesia  and  sulphates  low. 

The  specification  requires  that  a  pat  of  neat  cement  shall  be 
kept  in  moist  air  for  24  hours  and  then  exposed  for  5  hours  in  an 
atmosphere  of  steam  at  a  temperature  between  98  and  100 
degrees  Centigrade  on  a  suitable  support  1  in.  above  the  boiling 
water.  This  pat  of  neat  cement  should  be  about  3  in.  in  diameter, 
J^  in.  thick  at  the  center,  and  tapering  to  a  thin  edge.  To 
pass  the  soundness  test  successfully,  the  pat  should  remain  firm 
and  hard  and  should  show  no  signs  of  distortion,  checking,  crack- 
ing, or  disintegrating.  This  test  is  commonly  known  as  the 
"accelerated"  test. 

The  old  specifications  required  three  pats  to  be  tested.  One 
was  to  be  subjected  to  the  accelerated  test.  One  pat  was  to  be 
kept  in  moist  air  for  24  hours  and  then  in  water  for  27  days,  and 
observed  at  intervals.  The  third  pat  was  to  be  kept  in  moist 
air  for  24  hours  and  then  in  air  for  27  days,  and  observed  at 
intervals.  The  temperature  of  the  air  and  water  was  to  be  kept 
as  near  70  degrees  Fahrenheit  as  practicable. 


34  MATERIALS  OF  CONSTRUCTION 

37.  Strength. — The  tensile  strength  of  cement  has  but  little 
value  as  a  measure  of  the  suitability  of  the  cement  for  structural 
purposes,  but  it  is  of  value  as  a  means  of  comparing  different 
cements  and  also  because  of  the  relation  of  the  tensile  to  the 
compressive  strength.  While  the  ratio  of  tensile  strength  to 
compressive  strength  varies  for  different  cements  and  for  differ- 
ent ages,  it  is  generally  true  that  a  cement  that  is  strong  in 
tension  is  also  strong  in  compression.  Because  of  fewer  diffi- 
culties in  the  making  and  testing  of  specimens  and  because  of  the 
lower  cost  and  weight  of  testing  machines  required,  tension 
tests  have  been  standardized  in  preference  to  compression  tests 
on  cement. 

A  slight  increase  in  the  lime  content  increases  the  tensile 
strength  a  little.  Fine  grinding  increases  the  strength  of  cement 
mortar  but  not  that  of  the  neat  cement.  An  addition  of  more 
than  5  or  10  per  cent  of  clay  is  injurious.  Hydrated  lime  will 
decrease  the  strength  of  neat  cement.  A  high-tensile  strength 
does  not  indicate  that  the  cement  is  sound.  A  large  retrogression 
in  the  strength  of  cement  is  a  bad  sign. 

The  tensile  test  requirements  for  neat  cement  have  been  discon- 
tinued in  the  new  specifications.  The  following  are  the  old 
specifications  (minimum  requirements)  for  the  strength  of  neat 
cement : 

STRENGTH,  POUNDS 
STORAGE  PER  SQUARE  INCH 

1  day  in  moist  air 175 

1  day  in  moist  air  and  6  days  in  water 500 

1  day  in  moist  air  and  27  days  in  water 600 

The  compressive  strength  of  cement  is  the  best  criterion  to  use 
in  choosing  a  cement  for  structural  purposes,  but  for  several 
reasons  this  test  has  not  been  standardized.  The  compressive 
strength  of  a  good  neat  cement  is  about  10  times  its  tensile 
strength.  The  modulus  of  elasticity  for  cement  in  compression 
is  not  a  constant  because  the  stress  strain  curve  is  not  a  straight 
line  for  any  appreciable  portion  of  its  length.  The  compressive 
strength  of  cement  is  influenced  by  the  same  factors  as  the  tensile 
strength. 

The  shearing  strength  of  neat  cement  is  about  the  same  as  the 
tensile  strength,  and  it  depends  upon  the  same  factors.  Very 
little  information  regarding  the  shearing  strength  of  neat  cement 
is  available. 


PORTLAND  CEMENT  35 

38.  Time  of  Set. — One  of  the  most  important  properties   of 
Portland  cement  is  its  property  of  setting  and  hardening,  which 
is  caused  principally  by  the  hydration  of  its  three  major  con- 
stituents, tricalcium  silicate,  dicalcium  silicate,  and  tricalcium 
aluminate.    When  water  is  added  to  Portland  cement,   these 
compounds   first   form   amorphous   and   later   both   crystalline 
and  amorphous  hydrated  materials.    The  tricalcium  aluminate 
sets  and  hardens  very  quickly,  and  the  " initial"  set  of  the  cement 
is  undoubtedly  due  to  the  hydration  of  this   compound.    The 
early  hardness  and  cohesive  strength  of  the  cement  are  due  to 
the  hydration  of  the  tricalcium  aluminate  and  the  tricalcium 
silicate.     The  further  increase  in  strength  is  due  to  the  further 
hydration  of  these  two  compounds  as  well  as  that  of  the  dical- 
cium silicate.    The  tricalcium  silicate  is  the  most    important 
cementing  compound  of  the  three.     This  setting  and  hardening 
will  progress  under  water  as  well  as  in  air. 

The  actual  time  of  set  is  of  much  importance  in  some  work. 
It  is  not  desirable  to  have  the  set  occur  before  the  concrete  is 
placed,  neither  is  it  desirable  to  have  too  long  a  time  elapse 
before  the  cement  sets,  especially  if  the  cement  is  to  be  placed 
under  water.  In  general,  the  higher  the  temperature  the  quicker 
the  set  takes  place.  An  excess  of  water  will  lengthen  the  time 
required.  Cement  sets  slower  in  damp  weather  than  in  dry. 
An  addition  of  gypsum  or  plaster  of  Paris  up  to  about  3  per  cent 
retards  the  set,  while  a  larger  addition  of  plaster  of  paris  will  tend 
to  give  the  cement  a  " flash"  set.  The  seasoning  of  the  cement 
often  affects  the  time  of  set,  sometimes  increasing  and  sometimes 
decreasing  the  length  of  time  required. 

The  specifications  require  that  the  cement  shall  not  develop 
initial  set  in  less  than  45  minutes  when  the  Vicat  needle  is  used  or 
60  minutes  when  the  Gilmore  needle  is  used.  Final  set  shall  be 
attained  within  10  hours. 

39.  Fineness. — It  has  been  determined  that  the  final  particles 
of  cement  are  the  ones  which  give  the  cement  its  cementing 
values.     Fineness  of  grinding  increases  the  strength  of  cement 
mortars,  but  not  that  of  neat  cement  pastes.     Fine  grinding 
also  increases  the  sand  carrying  capacity  of  the  cement,  shortens 
the  time  of  set,  and  is  thought  to  make  the  cement  more  sound. 

The  specifications  for  fineness  of  cement  require  that  78 
per  cent  or  more  of  the  cement  shall  pass  a  standard  200-mesh 
sieve. 


36  MATERIALS  OF  CONSTRUCTION 

40.  Specific  Gravity. — The  specific  gravity  test  of  Portland 
cement  is  not  of  much  importance  and  is  not  made  unless  it  is 
specifically  ordered.     A  low  specific  gravity  may  be  caused  by 
adulteration  in  large  amounts,  but  small  amounts  may  not  have 
enough  effect  to  lower  the  specific  gravity  below  3.10.     There  is 
practically  no  relation  between  the  degree  of  burning  and  the 
specific  gravity.     Seasoning  tends  to  lower  the  specific  gravity, 
due  to  the  absorption  of  carbon  dioxide  and  moisture  from  the  air. 

The  specifications  require  that  the  specific  gravity  of  Portland 
cement  shall  not  be  less  than  3.10  (3.07  for  white  Portland 
cement).  Should  the  test  of  cement  as  received  fall  below  this 
requirement,  a  second  test  shall  be  made  upon  an  ignited  sample. 

41.  Uses  of  Portland  Cement. — At  present,  Portland  cement  is 
used  very  much  in  structural  work  and  it  is  rapidly  replacing 
lime,  natural  cement,  and  other  kinds  of  cements  in  this  field. 
As  a  part  of  mortar  it  is  used  for  stone  and  brick  masonry  and  for 
finishing  coats,  etc.     As  a  part  of  monolithic  concrete  it  is  used 
for  all  kinds  of  heavy  masonry  work  such  as  foundations,  dams, 
piers,  footings,  abutments,  retaining  walls,  pavements,  sidewalks, 
etc.     As  a  part  of  reinforced  concrete  it  is  used  in  walls,  buildings, 
floors,  roofs,  piles,  bridges,  tunnels,  subways,  ships,  conduits,  pipes, 
culverts,  etc.     Portland  cement  ranks  next  to  steel  and  timber 
as  a  structural  material  at  the  present  time  and  it  will  probably 
outrank  timber  in  the  near  future.     At  present,  cement  concrete  is 
not  so  reliable  a  structural  material  as  steel  or  timber,  due  to  the 
fact  that  not  so  much  is  known  about  concrete  and  also  that 
unskilled  men  are  often  employed  for  selecting  the  aggregate  and 
mixing   and  laying  of  the  concrete.     There  is   no  doubt  but 
that  the  use  of  Portland  cement  in  structural  work  will  be  much 
more  extensive  in  the  future  than  it  is  at  the  present  time. 


CHAPTER  IV 

PORTLAND  CEMENT  MORTARS 

A.  DEFINITIONS  AND  MATERIALS 

42.  Definitions. — A  Portland  cement  mortar  is  a  mixture  of 
Portland  cement,  fine  aggregate  (sand  or  its  equivalent),  and 
water. 

Fine  aggregates  are  particles  of  gravel,  crushed  stone,  sands, 
or  other  materials  which  will  pass  a  Y±  in.  sieve. 

Silt  is  sometimes  defined  as  particles  between  0.005  mm  and 
0.05  mm.  in  diameter;  clay  as  particles  less  than  0.005  mm.  in 
diameter;  and  loam  as  a  mixture  of  any  of  the  fine  materials 
with  organic  matter,  either  animal  or  vegetable. 

43.  The  Cement  and  the  Water. — The  cement  should  be  a 
Portland  cement  capable  of  passing  the  standard  specifications. 
On  the  work,  the  cement  should  be  stored  in  a  weather-tight 
building  which  will  protect  it  from  dampness,  and  so  piled  as  to 
permit  of  ready  inspection  and  sampling.     Whenever  practicable, 
each  shipment  of  cement  should  be  sampled  and  tested  before 
being  used. 

The  water  used  for  Portland  cement  mortar  should  be  free  from 
oils,  acids,  alkalis,  and  organic  matter  (either  animal  or  vegetable). 
The  water  should  not  contain  any  chemical  in  solution  that  would 
be  harmful  to  the  mortar.  The  presence  of  oil  is  easily  detected 
by  its  surface  film.  Organic  matter  (usually  of  vegetable  origin) 
can  sometimes  be  detected  by  observing  floating  particles,  or 
by  turbidity,  though  chemical  tests  are  often  required.  Tests  of 
water  for  acidity  or  alkalinity  can  be  made  by  means  of  litmus 
paper.  If  there  is  any  doubt  as  to  the  suitability  of  the  water  for 
use,  its  effect  on  soundness,  set,  and  strength  of  the  mortar 
should  be  determined  by  tests. 

44.  Sand  in  General. — In  mortars  and  concretes  it  is  just  as 
important  to  have  a  good  sand  as  it  is  to  have  a  good  cement. 
Due  to  the  progress  in  the  manufacture  of  Portland  cement,  the 
quality  of  most  Portland  cements  is  such  that  there  are  more 
failures  due  to  the  use  of  a  poor  sand  than  to  the  use  of  a  poor 
cement. 

37 


38  MATERIALS  OF  CONSTRUCTION 

The  sand  should  be  composed  of  a  hard  siliceous  material  free 
from  loam,  clay,  sticks,  animal  or  vegetable  matter,  friable 
materials,  etc. ;  and  the  particles  of  sand  should  be  small  enough 
to  pass  through  a  quarter  inch  sieve.  The  best  sand,  as  to  size, 
is  one  which  contains  both  coarse  and  fine  grains  in  such  propor- 
tions that  the  percentage  of  voids  will  be  a  minimum.  A  coarse 
grained  sand  is  usually  better  than  a  fine  grained  one.  While 
a  sand  should  preferably  consist  of  hard  silica  grains,  other 
minerals  may  be  present  without  causing  any  bad  effects.  How- 
ever, sands  containing  mica,  hornblende,  feldspar,  and  carbonate 
of  lime  are  not  durable  and  should  not  be  used.  The  physical 
condition  of  a  sand  is  of  more  importance  than  the  chemical  compo- 
sition. A  friable  sand  is  worthless.  A  small  percentage  of 
finely  divided  clay  or  loam  is  not  usually  injurious. 

Sands  may  be  washed  to  remove  dirt  and  like  materials,  but 
care  should  be  taken  not  to  wash  away  too  much  of  the  finer  parti- 
cles of  the  sand. 

45.  Properties  of  Sand. — Other  things  being  equal,  the  smaller 
the  percentage  of  voids,  the  better  the  sand  for  use  with  Portland 
cement.     The  percentage  of  voids  in  dry  sand  ranges  from  about 
25  to  45  per  cent.     The  percentage  of  voids  in  a  sand  may  be 
found  by  dropping  a  known  volume  of  well-shaken  dry  sand  into 
water  and  noting  the  volume  displaced.     The  difference  between 
the  original  volume  of  the  sand  and  the  volume  of  the  water 
displaced  gives  the  volume  of  voids.     Or,  as  the  specific  gravity 
is  nearly  a  constant  (2.65)  for  all  sands,  the  percentage  of  voids 
can  be  approximately  determined  from  the  weight  per  cubic 
foot.     Another  way  is  to  pour  water  on  the  sand  (contained  in  a 
water-tight  vessel)   until  the  surfaces  of  the  sand  and  water 
coincide.     The  volume  of  water  required  is  equal  to  the  volume 
of  voids  in  that  amount  of  sand. 

Well-shaken  dry  sand  will  weigh  from  90  to  125  Ib.  per  cubic 
foot,  but  if  the  sand  is  in  a  loose  condition  it  may  weigh  as  much 
as  20  per  cent  less. 

Moist  sand,  that  is  not  packed,  weighs  less  than  dry  sand. 

The  percentage  of  absorption  of  sand  rarely  exceeds  3  per  cent. 

The  specific  gravity  of  sand  is  usually  between  2.6  and  2.7  and 
the  average  value  is  about  2.65. 

46.  Sieve  Analysis  of  Sand. — The  sieve  analysis  of  sand  (or 
fine  aggregate)  is  one  of  the  best  tests  for  determining  the  suit- 
ability of  the  sand  for  use  in  a  Portland  cement  mortar.     This 


PORTLAND  CEMENT  MORTARS 


39 


analysis  consists  of  sifting  a  sample  of  sand  through  several  dif- 
ferent sieves  (five  or  more)  and  noting  the  amount  passing  each 
sieve.  Sieve  openings  Ko  in.  or  larger  are  usually  in  the  form 
of  circular  holes,  while  woven  brass  wire  cloth  is  used  for  the 
sieves  with  smaller  openings.  These  woven-wire  sieves  are 
known  by  numbers  corresponding  to  the  number  of  openings  per 
lineal  inch.  For  analyzing  sands  the  following  sieves  are 
desirable : 


Diameter 

Diameter 

Diameter 

Sieve 

of  opening, 

Sieve 

of  opening, 

Sieve 

of  opening, 

inches 

inches 

inches 

%in. 

0.375 

No.  10 

0.073 

No.  40 

0.015 

Mm. 

0.250 

No.  15 

0.046 

No.  50 

0.011 

H  in. 

0.167 

No.  20 

0.034 

No.  80 

0.007 

Ho  in. 

0.100 

No.  30 

0.022 

No.  100 

0.0055 

The  results  of  a  sieve  analysis  may  be  shown  graphically  by 
plotting  the  sieve  openings  as  abscissae  and  the  corresponding 
percentages  passing  each  sieve  as  ordinates.  This  will  give  a 
curve  from  which  the  qualities  of  the  sand  may  be  estimated 
(see  chapter  on  "Plain  Concrete"  for  sample  curves,  for  sand). 

The  uniformity  coefficient  is  the  ratio  of  the  diameter  of  the 
particles,  represented  by  the  point  where  the  curve  crosses  the 
60  per  cent  line,  to  the  diameter  of  the  particles  where  the  curve 
crosses  the  10  per  cent  line.  A  coarse  sand  has  a  uniformity 
coefficient  of  about  5.2  or  more;  a  medium  sand  of  about  4.2; 
and  a  fine  sand  of  about  2.2.  A  sand  that  has  a  uniformity 
coefficient  of  about  4.5  is  usually  considered  good  for  concrete 
work. 

47.  Standard  Sand. — Standard  sand  is  the  sand  recommended 
for  use  in  cement  testing  by  the  American  Society  of  Civil 
Engineers  and  other  engineering  societies.     It  is  a  natural  bank 
sand  obtained  from  Ottawa,  111.,  U.  S.  A.,  and  screened  to  proper 
size.     Only  the  sand  that  passes  a  No.  20  sieve  and  which  is 
held  on  a  No.  30  sieve  is  used.     The  percentage  of  voids  in  this 
sand  is  about  37  per  cent,  and  the  weight  per  cubic  foot  is  about 
104  Ib. 

48.  Substitutes    for    Sand. — Stone    screenings    are    the    fine 
materials  (less  than  one-quarter  of  an  inch  in  size)  which  have 


40 


MATERIALS  OF  CONSTRUCTION 


been  screened  out  from  crushed  stone.  When  they  are  free 
from  clay  and  dirt,  they  make  a  good  substitute  for  sand.  They 
are  apt  to  be  a  little  coarser  than  sand,  but  they  have  about  the 


0.0+      o.oe      o./2      o./6 

O/ometer  of  J/etv  Opening  in  fates 

FIG.   16. — Mechanical  analysis  of  sands. 


same  percentage  of  voids  and  weight  per  cubic  foot.  Screenings 
make  a  strong  mortar,  but  the  strength  usually  decreases  more 
rapidly  with  a  decrease  in  the  amount  of  cement  than  in  the  case 
of  a  sand  mortar. 

Well  selected  and  screened  mine  tailings  often  make  as  good  a 
cement  mortar  as  stone  screenings.  Granulated  blast-furnace 
slag,  small  cinders,  clay,  loam,  etc.  have  been  used  as  substitutes 
for  sand  in  a  Portland  cement  mortar,  but  they  do  not  make  so 
good  a  mortar  as  ordinary  sand. 

49.  Specifications  for  Fine  Aggregate. — These  specifications 
are  practically  the  same  as  those  adopted  by  the  New  York  Public 
Service  Commission.  Fine  aggregates  for  use  in  a  Portland 
cement  mortar  or  concrete  should  conform  to  the  following 
requirements. 


PORTLAND  CEMENT  MORTARS 
SIEVE  ANALYSIS  OR  MECHANICAL  GRADING 


41 


Sieve 

Diameter  of  opening, 
inches 

Per  c.ent  passing 
sieve  limits 

Kin. 

0.250 

100 

KG  in. 

0.187 

Between  93  and  100 

No.      6 

0.138 

Between  90  and  100 

No.    10 

0.073 

Between  75  and    93 

No.    15 

0.047 

Between  48  and    80 

No.    30 

0.022 

Between  20  and    50 

No.    50 

0.011 

Between    2  and    30 

No.  100 

0.0055 

Between    0  and      7 

Curves  for  the  extreme  conditions  may  be  plotted  upon  cross- 
section  paper  together  with  the  curve  for  the  sand  tested.  If  the 
sand  is  good,  its  curve  will  lie  between  the  two  extreme  curves. 
In  general,  a  sand  for  use  in  a  mortar  may  be  a  little  coarser  than 
a  sand  for  use  in  a  concrete. 

SiU. — Not  over  7  per  cent  of  the  dry  weight  of  the  sample 
should  pass  a  No.  100  sieve  when  screened  dry. 

Strength. — Both  tensile  and  compressive  strengths  of  a  1:3 
mortar  (proportioned  by  weight)  shall  be  equal  to  or  more  than 
the  strengths  required  for  a  1 : 3  standard  Ottawa  sand  mortar  in 
the  standard  and  tentative  (proposed)  specifications  of  the 
American  Society  for  Testing  Materials. 

Organic  Matter. — The  loss  on  ignition  shall  not  exceed  ^{Q  of 
1  per  cent  of  the  total  dry  weight. 

B.  PROPORTIONING  AND  MIXING  MORTAR 

50.  Proportioning  the  Mortar. — The  proportioning  of  cement 
and  sand  for  a  mortar  is  usually  done  by  one  of  the  three  following 
methods:  (1)  by  weight;  (2)  by  volumes  of  packed  cement  and 
loose  sand;  and  (3)  by  volumes  of  loose  cement  and  loose  sand. 

The  best  way  of  proportioning  the  materials  is  by  weight,  and 
this  method  is  usually  followed  in  the  laboratories,  though 
rarely  in  practical  work.  The  presence  of  moisture  in  the  sand 
may  affect  the  proportioning  to  some  extent  if  the  amount  of 
moisture  is  not  approximately  determined  and  allowed  for. 
Sand  rarely  contains  more  than  5  per  cent  of  moisture  by  weight ; 
hence,  the  error  due  to  moisture  would  usually  be  less  than  5  per 
cent  if  no  correction  were  made. 


42  MATERIALS  OF  CONSTRUCTION 

Proportioning  by  packed  cement  and  loose  sand  is  probably  the 
second  best  method.  This  method  is  used  to  some  extent  on 
practical  work.  Usually  a  sack  of  cement  is  considered  to  be 
1  cu.  ft.  in  volume  and  only  the  sand  is  measured.  In  measuring 
the  sand,  it  is  important  to  secure  the  same  degree  of  looseness 
each  time,  otherwise  the  proportions  may  be  changed.  The 
difference  in  volume  between  loose  and  compact  material  may  be 
as  much  as  20  per  cent  in  some  cases. 

Proportioning  by  loose  cement  and  loose  sand  measured  by 
volume  is  the  least  reliable  of  the  three  methods  due  to  the 
inability  or  neglect  of  the  average  workman  to  secure  the  same 
degree  of  compactness  at  all  times.  The  common  method  is  to 
dump  the  cement  and  sand  loosely  into  measuring  boxes  and  then 
empty  the  boxes  on  the  mixing  platform.  Often  the  measuring  is 
done  by  pails  or  wheelbarrows  and  the  proportioning  is  very 
inaccurately  done. 

The  proportions  of  mortar  for  masonry  work  are  usually  a  1 : 2 
or  a  1:3  mix,  1  part  of  cement  to  2  or  3  parts  of  sand.  Some- 
times as  rich  a  mix  as  a  1:1  is  required  for  finishing  or  other 
work  while  as  lean  a  mix  as  a  1:5  may  be  used  in  some  cases. 

51.  Mixing  the  Mortar. — The  mixing  should  be  done  either  by 
hand  or  by  machine.  In  either  method  it  is  better  first  to  mix 
the  cement  and  sand  dry  and  in  the  proper  proportions,  and  then 
add  the  water  and  mix  again.  The  batches  should  not  be  too  large. 

Machine  mixing  is  faster  than  hand  mixing  and  the  quality  is 
more  uniform.  The  cement  and  sand  are  first  placed  in  the 
machine  and  mixed  for  a  minute  or  so.  Then  the  water  is  added 
and  the  batch  mixed  for  a  few  minutes  more.  A  well-handled 
mixer  will  turn  out  a  batch  of  mortar  every  5  minutes. 

For  hand  mixing,  suitable  water-tight  platforms  must  be 
provided  to  prevent  the  loss  of  cement.  The  sand  is  first  spread 
out  in  a  layer  on  the  platform  and  the  cement  is  then  placed  in  a 
thin  layer  on  top  of  the  sand.  The  cement  and  sand  are  then 
mixed  dry  until  they  are  of  a  uniform  color.  Then  the  water  is 
added  and  the  batch  is  thoroughly  mixed  again.  Shovels  and 
hoes  are  convenient  tools  to  use  in  the  mixing.  Thoroughness  of 
mixing  is  of  the  most  importance. 

The  mortar  should  be  used  before  the  initial  set  has  taken  place. 
Cement  mortar  that  has  reached  initial  set  should  not  be  used. 
Retempering  (remixing)  of  cement  mortar  should  not  be  allowed 
after  the  initial  set  is  reached. 


PORTLAND  CEMENT  MORTARS  43 

C.  PROPERTIES  OF  PORTLAND  CEMENT  MORTARS 

52.  Strength  of  Portland  Cement  Mortars  in  General.— The 
strength  of  Portland  cement  mortar  depends  upon  (1)  the  pro- 
portion of  cement  used;  (2)  the  size  and  grading  of  the  sand;  (3) 
the  amount  of  water  used;  and  (4)  the  degree  of  compactness  of 
the  mortar.     That  is,  the  strength  of  the  mortar  depends  upon 
(a)  the  amount  of  cement  per  unit  volume,  and  (b)  the  density  of 
the  mortar. 

In  order  to  secure  the  best  results,  it  is  necessary  to  make  tests 
upon  different  mixes  of  cement,  sand,  and  water.  Uniform  condi- 
tions of  testing  must  be  carefully  observed  in  order  to  secure  relia- 
ble results.  The  strength  of  Portland  cement  mortar  is  affected  by 
the  temperature  of  the  air  and  water,  the  thoroughness  of  gaging, 
and  the  conditions  of  testing.  It  is  necessary  to  standardize  the 
methods  of  testing  before  trying  to  determine  the  influence  of 
the  constituents  of  the  cement,  sand,  and  water  used  in  the 
mortar.  This  testing  should  preferably  be  done  by  experienced 
operators  in  a  well-equipped  laboratory.  The  personal  equations 
of  different  operators  will  have  some  effect  on  the  results  and 
care  should  be  taken  to  minimize  this  effect  as  much  as  possible 
(see  any  book  on  the  testing  of  Portland  cement  and  cement 
mortars  for  the  standard  methods). 

53.  Effect  of  Density  and  Size  of  Sand  on  the  Strength. — 
Density  of  the  mortar  may  be  defined  as  the  ratio  of  the  actual 
solid  material  (absolute  volume  of  the  cement  and  sand)  to  the 
total  volume  of  the  hardened  mortar.     The  density  may  be 
determined  by  carefully  weighing  the  materials  used  and  assum- 
ing a  value  of  3.1  for  the  specific  gravity  of  the  cement  and  2.65 
for  the  specific  gravity  of  the  sand.     If  the  actual  values  for  the 
specific  gravities  have  been  obtained,  these  values  should  be  used. 

In  general,  the  size  and  grading  of  the  sand  that  will  give  the 
densest  mortar  will  also  give  the  strongest  mortar.  This  requires 
that  the  percentage  of  voids  shall  be  small  and  that  the  sand  shall 
have  a  sufficiency  of  coarse  grains.  A  low  percentage  of  voids 
depends  upon  the  grading  of  the  sand  and  not  on  the  actual  size 
of  the  grains.  With  the  same  percentage  of  voids,  a  coarse  sand 
will  make  a  stronger  mortar  than  a  fine  sand.  If  a  sand  is  not 
suitable  for  use,  it  may  be  made  suitable  by  mixing  another  sand 
or  part  of  another  sand  with  it  so  as  to  give  a  low  percentage  of 
voids.  Sometimes  a  sand  may  be  screened  in  two  or  three 


44  MATERIALS  OF  CONSTRUCTION 

different  sizes  and  these  sizes  remixed  in  different  proportions 
so  as  to  reduce  the  amount  of  voids. 

Feret  made  a  study  of  the  effect  of  the  size  of  sand  grains  on  the 
strength  of  Portland  cement  mortar  and  his  results  showed  that 
(1)  the  densest  mortar  was  generally  the  strongest;  (2)  the 
proportion  of  fine  sand  should  be  small;  and  (3)  if  the  sand  is 
uniform  in  size,  a  coarse  sand  is  better  than  a  medium  sand  and  a 
medium  sand  is  better  than  a  fine  sand. 

54.  Effect  of  the  Amount  of  Mixing  Water  on  the  Strength. — 
An  increase  in  the  amount  of  water  used   (above  the  proper 
amount  needed)  in  the  mixing  of  the  Portland  cement  mortar 
will  (1)  increase  the  time  required  for  setting;  (2)  decrease  the 
strength  of  neat  cement  mortar,  having  a  greater  effect  on  short 
time  than  on  long  time  tests;  (3)  decrease  the  strength  of  the 
mortar  on  short  time  tests  (say  under  6  months),  but  will  have 
less  effect  on  the  results  of  long  time  tests;   (4)   increase  the 
amount  of  laitance  on  the  surface;  (5)  increase  the  difficulty 
of  bonding  the  new  mortar  to  the  old;  and  (6)  tend  to  cause  a 
segregation  of  the  materials  (sand  and  cement). 

A  decrease  in  the  amount  of  water  (below  the  proper  amount 
required)  used  in  mixing  the  mortar  will  (1)  tend  to  hasten  the 
set;  (2)  increase  the  voids;  (3)  decrease  the  strength,  except  that 
a  slight  decrease  in  the  amount  of  water  used  may  increase  the 
strength,  especially  on  short  time  tests,  provided  that  the  mortar 
is  well  compacted;  and  (4)  make  the  mortar  less  water-tight. 

55.  Effect  of  Various  Conditions  on  the  Properties  of  Mortars. 
Mortars   made    and   used   in    dry   weather   should    have  their 
exposed  surfaces  kept  moist  for  several  days  so  that  the  water 
will  not  be  evaporated  from  these  surfaces  before  the  mortar 
has  hardened.     Portland  cement  rnortar  will  harden  a  little  more 
rapidly  in  dry  weather. 

Mortars  made  and  used  in  wet  weather  require  a  little  more 
time  to  set  and  attain  their  strength. 

Hot  weather  (high  temperatures)  decreases  the  time  required 
for  set  and  increases  the  rate  of  gain  in  strength. 

Low  temperatures  increase  the  length  of  time  required  for  the 
setting  and  hardening  of  the  cement  mortar  and  decrease  the 
strength  on  short  time  tests.  At  a  temperature  of  40  degrees 
Fahrenheit,  the  strength  is  only  about  two-thirds  of  that  at  70 
degrees  Fahrenheit  when  the  mortar  is  2  months  old.  Cement 
requires  about  four  times  as  long  to  set  at  a  temperature  of  32 


PORTLAND  CEMENT  MORTARS  45 

degrees  Fahrenheit  as  it  does  at  a  temperature  of  65  degrees 
Fahrenheit. 

Freezing  of  Portland  cement  mortars  retards  their  rate  of 
hardening  and  their  rate  of  increase  in  strength.  Exposed  sur- 
faces, that  are  frozen  before  the  final  set  occurs,  often  scale  off. 
It  is  not  good  practice  to  use  Portland  cement  mortar  in  freezing 
weather  unless  special  precautions  are  taken  to  keep  it  from 
freezing. 

Regaging  or  remixing  a  Portland  cement  mortar  after  setting 
has  begun  is  generally  not  permitted.  Experiments  on  the 
effect  of  regaging  mortars  gave  various  results,  depending  upon 
different  mortars  and  the  length  of  time  elapsed  between  the 
mixings.  Regaging  of  some  mortars  within  a  few  hours  after 
the  initial  set  had  taken  place  caused  no  bad  results  whatever, 
but  in  most  cases  such  regaging  seemed  to  cause  a  decrease  in 
the  ability  to  harden  as  well  as  a  decrease  in  the  strength.  It 
is  thought  that  the  effect  of  regaging  a  Portland  cement  mortar 
within  2  hours  after  mixing  is  not  very  injurious. 

56.  Effect  of  Various  Elements  on  the  Properties  of  Mortars. 
A  small  percentage  (2  or  3  per  cent)  of  mica  added  to  a  1:3 
Portland  cement  mortar  may  cause  a  20  per  cent  loss  of  strength 
due  to  an  increase  in  voids  and  the  inability  of  the  cement  to 
stick  to  the  smooth  surface  of  the  mica. 

Dirt  has  an  injurious  effect  on  the  strength  of  the  mortar, 
especially  if  it  contains  any  organic  matter. 

As  small  as  ^{Q  of  1  per  cent  of  organic  matter  may  be  injurious. 

A  small  percentage  of  any  friable  material  is  injurious. 

Clay  usually  decreases  the  strength  of  the  mortar,  but  in  some 
cases  a  small  amount  of  finely  divided  clay  (say  from  5  to  10 
per  cent),  which  has  been  thoroughly  mixed  with  the  sand, 
appears  to  have  a  good  effect.  A  rich  mortar  is  generally 
injured  by  the  addition  of  clay  while  a  lean  mortar  may  be 
improved,  especially  if  the  mortar  contains  a  large  percentage  of 
voids. 

Good  finely  divided  loam  has  about  the  same  effect  as  clay. 

Lime  has  about  the  same  effect  as  clay  but  is  not  thought  to  be 
so  injurious.  Small  percentages  of  lime  often  improve  a  lean 
mortar  but  may  injure  a  rich  mortar.  A  small  addition  of 
lime  paste  makes  a  cement  mortar  much  easier  to  work  with  in 
laying  brick  or  stone  masonry. 

Salt,  when  added  to  the  mixing  water,  lowers  the  freezing  point 


46  MATERIALS  OF  CONSTRUCTION 

of  the  mortar  and,  up  to  about  10  per  cent,  appears  to  have  but 
little  effect  on  the  strength.  For  temperatures  below  32  degrees 
Fahrenheit,  the  amount  of  salt  required  to  lower  the  freezing 
temperature  1  degree  Fahrenheit  is  about  1  per  cent  of  the  weight 
of  the  mixing  water. 

57.  Tensile   Strength. — The   statements   made   in   preceding 
paragraphs  on  the   strength   of   neat   Portland   cement  apply 
equally  well  to  the  strength  of  a  Portland  cement  mortar.     In 
determining  the  qualities  of  a  cement  that  is  to  be  used,  the  tensile 
strength  of  the  mortar  is  more  valuable  than  the  tensile  strength 
of  the  neat  cement.     Under  normal  conditions  the  strength  of 
Portland  cement  mortar  increases  very  rapidly  during  the  first 
few  days.     The  rate  of  gain  of  strength  gradually  decreases. 
At  the  age  of  7  days,  the  strength  is  about  one-half  or  two- 
thirds  of  the  maximum,  which  is  reached  at  an  age  of  about  3 
months.     The  specifications  (minimum  requirements)  for  a  1 : 3 
standard  sand  mortar  are  as  follows: 

ONE  PART  OF  PORTLAND  CEMENT  TO  3  PARTS  OF  STANDARD  OTTAWA  SAND 

TENSILE  STRENGTH, 
POUNDS  PER  SQUARE 
AGE  AND  STORAGE  INCH 

1  day  in  moist  air,  and    6  days  in  water 200 

1  day  in  moist  air,  and  27  days  in  water 300 

The  proportions  are  by  weight.  The  temperature  of  the 
materials  during  the  mixing,  storing,  and  testing  should  be  as 
near  70  degrees  Fahrenheit  as  practicable. 

A  good  sand  and  cement  should  give  results  much  higher  than 
the  above  minimum  requirements  for  a  standard  sand  mortar. 

Many  mortars  show  a  slight  retrogression  in  strength  after  5 
or  6  months,  but  this  retrogression  is  usually  not  permanent  and 
it  does  not  appear  at  all  in  the  compression  test  results. 

58.  Compressive  Strength. — Testing  a  Portland  cement  mortar 
in  compression  is  the  best  way  of  judging  of  the  suitability  of  the 
cement    and    sand    for    construction    purposes.     In    general,    a 
mortar  that  is  strong  in  tension  is  also  strong  in  compression, 
but  the  ratio  of  the  strengths  is  not  a  constant  quantity.     The 
compressive  strength  of  a  good  mortar  increases  steadily  with 
age  and  shows  no  retrogression. 

The  modulus  of  elasticity  in  compression  is  a  variable  quantity 
because  the  stress  strain  curve  is  not  a  straight  line.  At  about 
one-fourth  of  the  ultimate  strength,  the  modulus  of  elasticity 


PORTLAND  CEMENT  MORTARS  47 

in  compression  is  approximately  4,000,000  Ib.  per  square  inch 
for  neat  cement  and  about  3,000,000  Ib.  per  square  inch  for  a 
good  1:3  mortar. 

At  present  there  are  no  standard  specifications  for  the  com- 
pressive  strength  of  Portland  cement  mortar  in  America,  but 
the  following  minimum  requirements  have  been  proposed  and 
adopted  as  tentative  specifications: 

ONE  PART  OF  PORTLAND  CEMENT  TO  3  PARTS  OF  STANDARD  OTTAWA  SAND 

COMPRESSIVE  STRENGTH, 

POUNDS  PER  SQUARE 
AGE  AND  STORAGE  INCH 

1  day  in  moist  air,  and    6  days  in  water 1 , 200 

1  day  in  moist  air,  and  27  days  in  water 2 , 000 

The  specimens  are  cylinders  2  in.  in  diameter  and  4  in.  high. 
Each  value  should  be  the  average  of  not  less  than  three  specimens, 
and  the  average  at  28  days  must  be  higher  than  that  at  7  days. 

A  good  mortar  should  give  results  that  are  much  higher  than 
the  above  minimum  requirements  for  a  standard  sand  mortar. 

59.  Transverse     Strength. — The    transverse    strength    of    a 
Portland  cement  mortar,  as   calculated  from  the  formula  S  = 
Mv/I,  is  approximately  two  times  the   tensile  strength.     The 
cross-bending  strength  is  proportional   to  the  tensile   strength, 
and  it  depends  upon  the  same  factors. 

60.  Adhesive     Strength. — The    adhesive    strength    of    neat 
Portland  cement  and  Portland  cement  mortars,  at  the  age  of  6 
months,  with  a  few  different  materials,  is  shown  by  the  following 
table: 

ADHESIVE  STRENGTH  IN  POUNDS  PER  SQUARE  INCH 

MIXTURE  IRON  RODS  SAWN  LIMESTONE  BRICK 

Neat                          315                           270  50 

1:1                            290                           220  40 

1:2                           265                            170  30 

1:3                            110                             75  15 

61.  Shearing  Strength. — The  shearing  strength  is  of  import- 
ance, as  concretes  and  mortars  are  often  subjected  to  shearing 
stresses  in  practical  work.     Shearing  tests  are  rarely  ever  made 
on  account  of  difficulties  of  obtaining   a  true  shearing  stress. 
The   shearing  strength  depends  upon  the  same  factors  as  the 
tensile    and   compressive  strengths.     The  shearing  strength  is 
usually  proportional  to  the  compressive  strength.     The  fineness 


48  MATERIALS  OF  CONSTRUCTION 

of  grinding  of  the  cement  and  the  qualities  of  the  sand  are  the 
most  important  factors. 

The  following  table  gives  the  results  of  some  tests  upon  the 
shearing  strength  of  neat  Portland  cement  and  Portland  cement 
mortars  made  by  Bauschinger  in  1879.  The  specimens  were 
about  2%  by  5  in.  in  cross-section  and  were  stored  in  water. 
Each  result  is  an  average  of  nine  tests.  It  is  to  be  noted  that 
the  cement  used  did  not  pass  the  tension  test  requirements  of 
the  American  specifications;  the  neat  strength  being  224  Ib. 
per  square  inch  for  the  7-day  and  294  Ib.  per  square  inch  for  the 
.28-day  tests,  while  the  1 : 3  mortar  results  were  95  Ib.  per  square 
inch  for  the  7-day  and  169  Ib.  per  square  inch  for  the  28-day  tests. 

SHEARING  STRENGTH  IN  POUNDS  PER  SQUARE  INCH 

Mix  AGE  7  DAYS  AGE  28  DAYS  AGE  2  YEARS 

Neat  271  346  415 

1:3  116  188  375 

1:5  77  131  364 

62.  Miscellaneous  Properties. — Abrasive  resistance  of  Port- 
land cement  mortars  depends  not  only  upon  the  cement  but  also 
upon  the  hardness  of  the  sand  grains. 

Expansion  and  Contraction.— -Cement  mortar,  when  hardening, 
in  air,  will  contract  slightly,  and  when  hardening  in  water  it 
will  keep  a  nearly  constant  volume  or  expand  a  little.  The  richer 
the  mortar,  the  greater  the  effects  of  expansion  and  contraction. 

Permeability  is  the  measure  of  the  rate  of  flow  of  water  through 
a  mortar  of  a  given  thickness  and  under  a  given  pressure.  An 
impermeable  mortar  is  a  water-tight  one.  Permeability  de- 
creases rapidly  for  all  mixtures  with  an  increase  in  the  age  of  the 
specimens  tested;  it  decreases  considerably  with  a  continuation 
of  flow;  and  it  increases  with  an  increase  of  pressure,  leanness 
of  mix,  dryness  of  mixture,  and  with  increased  coarseness  of  the 
sand  used.  An  addition  of  a  small  amount  of  finely  divided 
clay  or  loam  tends  to  decrease  the  permeability.  (See  the 
articles  on  "Impervious  Concrete"  in  the  chapter  on  "Plain 
Concrete"  for  methods  and  materials  for  decreasing  the  permea- 
bility of  plain  concrete.  These  articles  apply  to  a  Portland 
cement  mortar  as  well  as  to  plain  concrete.) 

Absorption  of  water  by  a  Portland  cement  mortar  depends 
upon  the  same  conditions  (but  not  to  so  large  an  extent)  as  the 
permeability  does.  In  general,  the  absorption  decreases  slightly 


PORTLAND  CEMENT  MORTARS  49 

with  age;  increases  with  an  increased  leanness  of  mixture;  and 
the  dry  mixtures  are  slightly  more  absorptive  than  the  wet  ones. 

Voids  in  a  Portland  cement  mortar  depend  upon  the  grading 
of  the  materials  and  the  consistency  of  the  mix.  A  well-graded 
aggregate  with  a  small  percentage  of  voids  will  usually  give  a 
mortar  with  a  small  percentage  of  voids.  If  more  or  less  water 
is  used  than  is  necessary  to  form  a  proper  consistency,  the  voids 
in  the  mortar  will  be  increased.  A  dry  mix  usually  has  more 
voids  than  a  corresponding  wet  mix.  The  voids  in  a  mortar 
usually  vary  between  15  and  30  per  cent. 

Weight. — A  good  Portland  cement  mortar  of  a  1 : 3  mix  will 
weigh  about  140  Ib.  per  cubic  foot;  a  1:1  mix  about  145  lb.; 
and  a  1:4  mix  about  138  lb.  per  cubic  foot.  The  weight  per 
cubic  foot  varies  directly  with  the  density  of  the  mortar  and  the 
specific  gravities  of  the  cement  and  fine  aggregate  used. 


CHAPTER  V 

PLAIN  CONCRETE 

A.  DEFINITIONS  AND  MATERIALS 

63.  Definitions. — Concrete  is  an  artificial  stone  made  by  mixing 
cement,  water,  and  an  aggregate  consisting  of  large  and  small 
particles,  such  as  broken  stone  or  gravel  and  sand  or  screenings. 

Aggregates  are  those  inert  materials  which,  when  bound 
together  by  cement,  form  a  concrete. 

Fine  aggregate  is  usually  defined  as  the  material  that  will  pass 
a  J£-in.  sieve,  while  coarse  aggregate  is  the  material  which  is 
held  on  a  J^-in.  sieve. 

64.  Cement,    Water,    and    Fine    Aggregate. — Cement. — The 
cement  used  should  preferably  be  a  Portland  cement  that  will  pass 
the  standard  specifications  of  the  American  Society  for  Testing 
Materials  (or  equivalent  specifications)  when  subjected  to  the 
standard  tests  recommended  by  the  American  Society  of  Civil 
Engineers.  .  . 

After  delivery  at  the  work,  the  cement  should  be  carefully 
stored  in  weatherproof  buildings  having  tight  floors  above  the 
ground  level  in  order  to  protect  the  cement  from  the  weather  and 
to  allow  of  ample  time  for  inspection  and  testing.  If  kept  dry, 
the  cement  will  not  be  injured  by  a  long  storage  and  it  may  be 
improved,  due  to  the  seasoning.  Before  being  used,  each 
shipment  of  cement  should  be  carefully  inspected,  sampled,  and 
tested  by  a  competent  person.  In  sampling,  one  sample  should 
be  taken  from  about  every  tenth  barrel  and  care  should  be  taken 
to  secure  a  fair  sample.  The  amount  of  cement  required  for  the 
standard  tests  is  about  10  Ib. 

Water. — The  water  used  in  making  concrete  should  be  clean  and 
free  from  any  impurities  which  would  be  injurious  to  the  concrete. 
See  the  discussion  regarding  a  suitable  water  for  Portland  cement 
mortars  in  the  preceding  chapter  (Chap.  IV,  Art.  43). 

Fine  Aggregate. — The  fine  aggregate  used  in  making  concrete 
should  be  a  good  sand,  or  its  equivalent,  and  should  possess 
those  requisites  that  are  given  and  discussed  in  the  preceding 
chapter  (Chap.  IV)  on  "Portland  Cement  Mortars."  In  general 

51 


52  MATERIALS  OF  CONSTRUCTION 

a  sand  for  use  in  a  concrete  should  possess  more  fine  particles 
than  a  sand  for  use  in  a  Portland  cement  mortar. 

The  fine  aggregate  should  be  stored  in  bins  or  piles  convenient 
to  the  work  and,  if  necessary,  be  screened  to  remove  large  particles 
and  be  washed  to  remove  dirt  and  silt.  In  washing,  care  should  be 
taken  not  to  wash  out  too  much  of  the  finer  material. 

65.  Coarse  Aggregate  in  General. — The  coarse  aggregate  used 
for   concrete  usually  consists  of  crushed  stone,  gravel,  cinders, 
slag,  broken  brick,  etc.     Any  stone  is  suitable  for  concrete  work 
that  is  durable  and  strong  enough  so  that  the  strength  of  the  con- 
crete will  not  be  limited  by  the  strength  of  the  stone.     Strength, 
density,    hardness,    toughness,    durability,    and    cleanliness    are 
desirable    properties   in    a    coarse  aggregate.     As  the   physical 
character  of  a  rock  depends  upon  its  mineral  constituents  and 
structure,  only  those  rocks  which  have  durable  mineral  constit- 
uents and  a  dense,  strong  structure  should  be  used  for  concrete. 
Rocks  which  are  structurally  weak  or  which  contain  weak  mineral 
constituents  should  not  be  used.     Granites,   traps,   and   lime- 
stones are  often  employed  for  concrete  work,  while  sandstones 
are  rarely  suitable  for  this  work.     Soft,  flat,  or  elongated  particles 
do  not  make  a  satisfactory  material  for  use  in  concrete.     Clean 
screened  gravel  is  a  good  substitute  for  broken  stone,  but  it 
often  contains  some  particles  of  a  soft  friable  nature  that  will 
reduce  the  strength  of  the  concrete.     Cinders,  and  sometimes 
slag,  may  be  used  for  a  coarse  aggregate  for  a  concrete  subjected 
to  very  low  stresses  or  which  may  be   used  as  a  fireproofing 
material  or  where  light  weight  is  desired.     Broken  brick  should 
not    be    used  in   concrete   work   of   any   importance   or   where 
strength  is  required. 

After  the  stone  is  quarried,  it  may  be  broken  by  laborers  with 
stone  hammers  or  it  may  be  crushed  in  stone  crushers.  Jaw 
crushers  are  usually  used  in  small  or  portable  plants  and  gyratory 
crushers  in  large  stationary  plants  Screening  of  the  crushed 
stone  or  gravel  is  often  necessary  to  remove  the  dust  and  other 
fine  material  that  will  pass  a  ^i-in.  sieve.  Sometimes  it  is  neces- 
sary to  wash  the  gravel  to  remove  the  dirt,  loam,  clay,  or  organic 
matter  adhering  to  it. 

Coarse  aggregate  may  be  stored  in  bins  or  piled  in  the  open 
without  any  special  protection  from  the  weather.  Care  should 
be  taken  to  keep  the  coarse  aggregate  clean  and  prevent  dirt, 
clay,  loam,  organic  matter,  etc.  from  being  mixed  with  it. 

66.  Size  of  Coarse  Aggregate. — The  maximum  size  of  crushed 


PLAIN  CONCRETE  53 

stone  for  concrete  work  varies  according  to  the  use  to  which  the 
concrete  is  to  be  put.  When  crushed  stone  is  used  for  massive 
walls,  the  maximum  size  may  be  2^  or  3  in.;  2  in.  for  abutments; 
1J4  in.  for  arch  rings;  1  in.  for  copings,  bridge  seats,  and  thin 
walls;  and  1  in.  or  %  in.  for  reinforced  concrete  work.  Flat,  ir- 
regular, or  rough  stones  are  not  so  desirable  as  are  the  more 
rounded  ones. 

A  crushed  stone  or  gravel  that  is  nearly  all  of  one  size  is  not  so 
good  as  an  aggregate  that  is  made  up  of  uniformly  graded  parti- 
cles because  an  aggregate  all  of  one  size  usually  has  a  larger  per- 
centage of  voids.  It  is  often  desirable  to  screen  the  aggregate 
into  two  or  more  sizes  and  remix  these  sizes  in  different  proportions 
in  order  to  secure  the  proper  grading. 

A  mechanical  (sieve)  analysis  is  of  value  in  studying  the  grading 
of  a  coarse  aggregate  that  is  to  be  used  in  concrete  work.  The 
sieves  used  are  preferably  ones  of  2J^-,  2-,  1%-,  lM->  lJ^->  1-, 
%->  M->  %->  and  34-in.  mesh.  Usually  all  of  these  sieves  are 
not  needed  for  any  one  test,  but  just  a  sufficient  number  should  be 
used  to  give  the  desired  information.  The  results  of  a  sieve 
analysis  may  be  plotted  on  cross-section  paper  and  a  curve 
drawn  through  the  points  (see  article  on  "  Proportioning  by 
Mechanical  Analysis"  for  further  discussion). 

67.  Voids,  Weight  per  Cubic  Foot,  and  Specific  Gravity 
of  Coarse  Aggregates. — The  voids  in  a  coarse  aggregate  may  be- 
found  by  pouring  a  known  volume  of  the  aggregate  into  a  known 
volume  of  water  and  noting  the  displacement.  In  measuring 
the  volume  of  the  aggregate,  care  must  be  taken  to  secure  a  uni- 
form degree  of  compactness.  The  volume  of  the  aggregate  minus 
this  displaced  volume  equals  the  volume  of  the  voids. 

Another  way  of  determining  the  voids  in  a  coarse  aggregate  is  to 
pour  water  on  a  known  volume  of  the  aggregate,  contained  in  a 
water-tight  vessel,  until  the  surfaces  of  the  aggregate  and  the 
water  coincide.  The  volume  of  the  water  added  equals  the 
volume  of  the  voids. 

The.  percentage  of  voids  varies  from  30  to  55  per  cent  for  com- 
mon crushed  stone  and  gravel,  depending  to  some  extent  on  the 
shape,  grading,  and  degree  of  compactness. 

The  weight  per  cubic  foot  for  coarse  aggregate  (crushed  stone 
and  gravel)  usually  varies  from  about  75  to  120  Ib.  Crushed 
stone  is  often  sold  by.  the  cubic  yard  but  it  is  frequently  measured 
by  weight,  2,500  Ib.  being  considered  equal  to  1  cu.  yd. 


54 


MATERIALS  OF  CONSTRUCTION 


The  specific  gravity  of  stone  and  gravel  varies  somewhat. 
Approximate  values  are  as  follows:  trap  2.8  to  3.0;  granite  2.65 
to  2.75;  limestone  2.6  to  2.7;  sandstone  2.3  to  2.6;  and  ordinary 
sand  and  gravel  2.6  to  2.7. 

The  following  table  shows  the  relation  between  voids,  weight 
per  cubic  foot,  and  specific  gravity: 

VOIDS  AND  WEIGHT  OF  BROKEN  STONE  AND  GRAVEL 


Percentage 
of  voids 

Weight  in  pounds  per  cubic  foot 

Specific 
gravity 
2.6 

Specific 
gravity 

2.7 

Specific 
gravity 
2.8 

Specific 
gravity 
2.9 

Specific 
gravity 
3.0 

35 

106 

110 

114 

118 

122 

40 

97 

101 

105 

109 

112 

45 

89 

93 

96 

100 

103 

50 

81 

84 

87 

91 

94 

55 

73 

76 

79 

82 

84 

68.  Specifications  for  Coarse  Aggregate. — The  following  speci- 
fications are  those  of  the  American  Railway  Engineering  and 
Maintenance  of  Way  Association: 

Stone  shall  be  round,  hard,  and  durable,  and  shall  be  crushed  to 
sizes  not  exceeding  2  in.  in  any  direction.  For  reinforced  con- 
crete, sizes  usually  are  not  to  exceed  %  in.  in  any  one  direction, 
but  the  size  may  be  varied  to  suit  the  character  of  the  reinforcing 
materials. 

Gravel  shall  be  composed  of  clean  pebbles  of  hard  and  durable 
stone  of  sizes  not  exceeding  2  in.  in  diameter,  and  shall  be  free 
from  clay  and  other  impurities  except  sand.  When  the  gravel 
contains  sand  in  any  considerable  quantity,  the  amount  of  sand 
per  unit  of  volume  of  the  gravel  shall  be  determined  accurately, 
to  admit  of  the  proper  proportion  of  sand  being  maintained  in  the 
concrete  mixture. 

The  following  specifications  for  coarse  aggregate  for  concrete 
are  practically  the  same  as  those  adopted  by  the  New  York  Public 
Service  Commission. 

Cleanliness. — All  broken  stone  aggregate  must  be  so  free  from 
dust  that  the  limit  of  fineness  (5  per  cent)  shall  not  be  exceeded 
(fine  material  being  the  material  passing  the  ^-m.  sieve).  All 
gravel  must  be  thoroughly  washed,  preferably  at  the  plant  or  pit 
where  it  is  secured. 


PLAIN  CONCRETE  55 

Mechanical  Grading. — A  sieve  analysis  shall  be  made  of  the 
coarse  aggregate  and,  if  the  aggregate  is  suitable  for  use,  the 
results  should  be  within  the  limits  given  in  the  following  table. 
If  so  desired,  curves  for  the  extreme  conditions  or  limits  for  the 
kind  of  sieves  used  may  be  plotted  on  cross-section  paper  together 
with  the  curve  for  the  coarse  aggregate  tested.  If  the  coarse 
aggregate  is  good  for  use,  its  curve  will  lie  between  the  two 
extreme  or  limiting  curves. 

MECHANICAL  GRADING 

SIZE  OF  SQUARE-HOLED  SIEVES,  LIMITS,   ROUND-HOLED  SIEVES,  LIMITS, 

OPENING,  PERCENTAGE  PASSING  PERCENTAGE  PASSING 
INCHES 

2  100  100 

1>£  Between  95  and  100  Between  75  and  95 

\Y±  Between  65  and    92  Between  50  and  85 

1  Between  40  and    80  Between  35  and  70 

%  Between  25  and    60  Between  20  and  50 

>£  Between  10  and    40  Between    7  and  35 

%  Between    0  and      5  Between    0  and    5 

B.  PROPORTIONING  OF  CONCRETE 

69.  General  Theory. — The  theory  of  proportioning  is  that  the 
fine  and  the  coarse  materials  should  be  so   proportioned  that 
the  concrete  will  have  the  greatest  density.     This  means  that  the 
voids  in  the  concrete  should  be  a  minimum.     This  is  accomplished 
when  there  is  just  enough  cement  to  fill  the  voids  in  and  com- 
pletely coat  all  of  the  particles  of  the  sand,  and  just  enough 
mortar  to  fill  all  the  voids  in  and  completely  coat  all  of  the 
particles  of  the  coarse  aggregate.     There  must  be  no  excess  of 
water,  otherwise  water  voids  will  be  formed. 

Proportioning  by  weight  will  secure  more  uniform  mixtures 
than  proportioning  by  volume  because  the  errors  due  to  the 
measurement  of  the  materials  in  a  loose  or  compact  form  are 
eliminated.  These  errors  may  be  as  large  as  20  per  cent.  In 
practical  work  the  proportioning  is  nearly  always  done  by  volume 
because  this  method  is  more  convenient. 

70.  Proportioning  by  Standard  Proportions. — Proportioning  in 
practical  work  is  commonly  done  by.  "rule  of  thumb,"  using 
certain  standard  proportions.     The  materials  are  measured  by 
volume,  the  unit  of  measurement  being  1  cu.  ft.  usually.     The 
following  are  some  of  the  standard  mixes: 


56  MATERIALS  OF  CONSTRUCTION 

1:1:2       A  very  rich  mixture  used  only  where  great  strength  and  water 

tightness  are  required. 
1: 1^:3  A  rich  mixture  not  quite  so  strong  as  the  first,  but  used  for  the 

same  purposes. 
1:2:4       A  good  mixture  used  very  often  in  reinforced  concrete  work  and 

for  foundations  subjected  to  vibrations. 
1:2^:5  A  medium  mixture  used  for  floors,  retaining  walls,  abutments, 

etc. 
1:3:6       A   lean   mixture   used   for  massive   concrete   structures   under 

steady  loads  of  not  great  intensity. 
1:4:8       A  very  lean  mixture  used  only  for  massive  concrete  work  which 

is  not  very  important. 

71.  Proportioning  with  Reference  to  Coarse  Aggregate. — The 

theory  of  this  method  is  that  just  enough  mortar  should  be  used 
to  fill  the  voids  in  the  coarse  aggregate.  In  practice,  more  mortar 
is  required,  because  of  the  separation  of  the  coarse  aggregate  by 
the  mortar  and  excess  water  and  the  consequent  increase  in  the 
voids.  About  10  per  cent  more  mortar  is  required  on  an  average. 
If  care  is  taken  to  secure  a  properly  graded  coarse  aggregate,  the 
voids  will  be  less,  and  less  mortar  will  be  required  to  produce  a 
concrete  of  the  required  strength  and  imperviousness.  This 
means  a  saving  of  cement  and  sand.  In  general,  ordinary 
proportioning  by  voids  is  no  better  than  arbitrary  proportioning, 
because  of  the  behavior  of  the  different  materials  when  mixed 
together  to  form  a  concrete. 

72.  Proportioning  with  Reference  to  Mixed  Aggregate. — The 
theory  of  this  method  is  to  grade  both  the  coarse  and  the  fine 
aggregates  together  so  as  to  reduce  the  percentage  of  voids  in 
the  mixture  to  a  minimum.     Then  the  amount  of  cement  required 
will  depend  upon  the  strength  and  imperviousness  desired.     The 
amount  of  cement  necessan^  to  fill  completely  the  voids  of  the 
mixture  may  be  estimated  by  making  a  void  test  on  a  well 
shaken  mixture  of  the  aggregates.     In  practical  work  it  has  been 
found  that  slightly  more  cement  is  required  to  make  a  concrete 
of  maximum   density   because   of  the   slight  increase  in   voids 
formed  when  the  cement  and  water  are  added.     This  method  is 
no  better  than  the  preceding  one. 

73.  Proportioning  by  Maximum  Density  Tests. — Different 
mixtures  of  fine  and  coarse  aggregates  may  be  mixed  with  the 
required  amounts  of  cement  and  water  and  the  resulting  concrete 
tested  to  determine  which  proportions  of  fine  and  coarse  aggre- 
gates are  the  best. 


PLAIN  CONCRETE  57 

The  procedure  of  the  test  is  roughly  as  follows:  A  trial  mix  of 
fine  and  coarse  aggregates  is  prepared,  the  proper  amounts  of 
cement  and  water  are  added,  and  the  whole  thoroughly  mixed. 
The  resulting  concrete  is  placed  in  a  water-tight  metal  cylinder 
and  tamped.  Then  the  volume  of  the  concrete  is  measured. 
Other  trial  mixes  of  the  fine  and  the  coarse  aggregates  are  pre- 
pared and  the  volumes  of  the  concretes  formed  are  carefully 
measured.  The  same  amounts  of  cement  and  water  should  be 
used  each  time  and  the  total  weight  of  all  materials  and  water 
should  be  the  same  for  all  of  the  tests. 

The  mixture  which  gives  the  least  volume  is  the  best  mixture 
and  will  make  the  strongest,  densest,  and  most  impervious 
concrete. 

Care  should  be  taken  not  to  use  too  much  water  when  making 
the  tests  as  the  excess  water  will  increase  the  voids  in  the  concrete 
and  thus  destroy  the  accuracy  of  the  tests. 

The  test  described  above  is  usually  called  a  "yield"  test  on 
concrete. 

74.  Proportioning  by  Mechanical  Analysis. — This  is  a  good 
and  accurate  method  of  properly  proportioning  the  concrete 
materials.  A  sieve  analysis  is  first  made  of  each  of  the  aggre- 
gates and  the  results  plotted  on  cross-section  paper,  using  the 
percentages  passing  a  given  sieve  as  ordinates  and  the  cor- 
responding sizes  of  sieve  openings  as  abscissae.  A  curve  is  drawn 
for  each  aggregate.  It  is  not  necessary  to  draw  a  curve  for  the 
cement  as  it  completely  passes  practically  all  of  the  sieves. 

By  using  the  curves,  the  materials  can  be  so  proportioned  (by 
cut  and  try  methods)  that  they  will  give  a  mechanical  analysis 
curve  that  agrees  very  closely  with  the  ideal  curve,  or  curve  of 
maximum  density.  This  ideal  curve  consists  of  a  portion  of  an 
elliptic  curve  and  a  straigh't  line.  The  straight  line  is  drawn 
from  the  intersection  of  the  maximum  size  of  the  coarse  aggregate 
and  the  100  per  cent  lines  tangent  to  an  elliptical  curve.  The 
ordinate  of  this  point  of  tangency  is  equal  to  33  per  cent,  and  the 
abscissa  is  equal  to  Jio  of  the  maximum  size  of  the  coarse  aggre- 
gate. The  elliptical  curve  is  drawn  from  this  point  of  tangency 
to  the  origin.  Aggregates  of  apparently  unsuitable  grading  may 
be  studied  in  this  way  and  the  proper  proportions  determined. 
Sometimes  it  is  found  necessary  to  screen  a  coarse  aggregate  into 
two  or  more  sizes  and  then  to  combine  these  sizes  in  different 
proportions  in  order  to  obtain  a  dense  mixture. 


58 


MATERIALS  OF  CONSTRUCTION 


75.   Example    of   Proportioning    by  Mechanical  Analysis. — 
Suppose  that  for  a  1:9  concrete,  it  is  desired  to  find  the  proper 


r4^ 


Diameter  of  sieve  opening  in  inches 
FIG.   17. — Mechanical  analyses  curves,  etc. 

proportions  of  sand  and  stone  whose  sieve  analysis  gave    the 
following  results: 


Sand 


Stone 


Sieve 

Per  cent  passing 

Sieve 

Per  cent  passing 

Hm. 

100 

2      in. 

100 

No.     6 

95 

11A  in. 

90 

No.     10 

86 

IK  in. 

65 

No.     15 

66 

1      in. 

54 

No.    30 

34 

%  in. 

32 

No.    50 

17 

Yz  in. 

18 

No.  100 

5 

Hin- 

3 

The  sieve-analysis  curves  for  the  aggregates  and  the    ideal 
curve   as  directed  in  the  preceding  article  should  be    plotted. 
A  tabulation  similar  to  the  following  should  then  be  made: 

CONCRETE  1:9  Mix  PER  CENT  PASSING  SIEVES 


Material 

No.  30 

No.  15 

No.  10 

No.  6 

K  in. 

Min. 

H  in- 

1  in. 

IK  in- 

IK  in. 

2  in. 

Cement.  . 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

Sand  

19^ 

22^ 

22^ 

22H 

22^ 

22K 

22^ 

22  H 

Stone 

y<t 

3 

36  M 

67K 

Total  .  . 

30 

35^ 

69 

100 

PLAIN  CONCRETE  59 

Because  of  lack  of  uniformity  in  the  grading  of  the  materials 
and  possible  errors  in  the  sieve  analysis,  computations  of  the 
percentages  to  the  nearest  H  P61*  cent  will  be  of  more  than 
sufficient  accuracy  for  the  problem. 

The  proportion  of  cement  in  a  1:9  mix  is  Ho  or  10  per  cent  of 
the  whole,  and  as  all  of  the  cement  will  pass  all  of  the  sieves  in 
the  tabulation  10  per  cent  may  be  written  for  all  values  for  the 
cement. 

To  obtain  the  proportions  for  the  first  trial  curve,  the  per- 
centage where  the  ideal  curve  crosses  the  Ji-in.  sieve  opening  line 
should  be  noted.  (This  is  about  35  per  cent  in  this  case.) 
Then  the  sum  of  the  cement,  sand,  and  stone  passing  this  sieve 
should  equal  about  35  per  cent.  As  the  cement  is  10  per  cent 
(see  tabulation),  25  per  cent  is  left  for  the  sand  and  stone.  As  all 
of  the  sand  passes  the  }/±-m.  sieve  and  only  3  per  cent  of  the 
stone,  22.5  per  cent  may  be  taken  for  the  sand.  Then  the 
proportions  for  the  first  trial  curve  will  be  1  part  (10  per  cent) 
cement,  2J4  parts  (22.5  per  cent)  sand,  and  6%  parts  (67.5  per 
cent)  stone. 

Now,  as  all  of  the  sand  passes  the  M~in-  and  larger  sieves, 
22.5  per  cent  may  be  written  in  the  tabulation  for  the  values  of 
the  sand  passing  these  sieves. 

The  amount  of  stone  passing  the  J^-in.  sieve  (expressed  as  a 
percentage  of  the  dry  materials)  is  determined  by  taking  67.5  per 
cent  of  3  per  cent  (see  sieve  analysis),  which  gives  about  2  per  cent. 

The  total  amount  of  dry  materials  passing  the  M-in-  sieve  is 
34.5  per  cent. 

Suppose  that  the  total  percentage  passing  the  1-in.  sieve  is 
next  determined.  There  will  be  10  per  cent  cement,  22.5  per 
cent  sand  (see  tabulation),  and  67.5  per  cent  of  54  per  cent  (see 
sieve  analysis)  or  36.5  per  cent  stone,  giving  a  total  of  69  per  cent. 

Suppose  that  the  total  percentage  passing  the  No.  10  sieve  is 
determined  next.  There  will  be  10  per  cent  cement  (see  tabula- 
tion), 22.5  per  cent  of  86  per  cent  (see  sieve  analysis)  or  19.5  per 
cent  sand,  and  67.5  per  cent  of  about  1  per  cent  or  approximately 
0.5  per  cent  stone,  giving  a  total  of  30  per  cent.  (For  the  smaller 
sieves,  no  harm  will  be  done  if  the  percentage  of  stone  passing  is 
neglected  as  the  values  will  be  less  than  0.5  per  cent  in  this 
problem.) 

In  the  same  way,  the  total  percentages  passing  all  of  the  other 
sieves  should  be  determined  and  recorded  in  the  tabulation. 


60  MATERIALS  OF  CONSTRUCTION 

Then  all  of  these  total  percentages  should  be  plotted  and  a 
smooth  curve  drawn  through  the  points. 

If  the  trial  curve  agrees  very  closely  with  the  ideal  curve,  the 
proportions  chosen  are  correct. 

If  the  trial  curve  is  mostly  above  the  ideal  curve,  the  proportion 
of  sand  should  be  decreased  and  the  proportion  of  stone  increased 
and  a  new  trial  curve  computed  and  plotted. 

If  the  trial  curve  is  mostly  below  the  ideal  curve,  the  propor- 
tion of  sand  should  be  increased  and  the  proportion  of  stone 
decreased  and  a  new  trial  curve  computed  and  plotted. 

The  process  should  be  continued  until  a  satisfactory  curve  is 
obtained  or  the  materials  are  found  to  be  unsuitable  as  they  are. 
An  experienced  operator  rarely  has  to  make  more  than  three  trial 
curves. 

For  a  good  working  concrete,  the  total  percentages  passing  the 
smaller  sieves  should  not  fall  below  the  ideal  curve,  as  it  is  better 
to  have  a  slight  excess  of  fine  material  than  to  have  too  little  of 
it.  In  regard  to  the  total  percentages  passing  the  larger  sieves, 
it  is  immaterial  whether  the  trial  curve  is  a  little  above  or  a  little 
below  the  ideal  curve. 

A  complete  solution  of  the  above  problem  should  be  made 
so  that  the  method  may  be  thoroughly  understood. 

76.  Proportioning  of  Concrete  Mixes  by  Abrams'  Method.1— 
This  method  is  probably  the  most  scientific  method  of  concrete 
proportioning  yet  proposed  as  it  is  based  on  fairly  definite  rela- 
tions between  the  sieve  analysis  of  the  aggregate,  the  consistency 
of  the  mix,  and  the  strength  of  the  concrete.  It  is  frequently 
called  the  "  fineness  modulus  method." 

The  fundamental  principle  of  this  method  is  that,  other  things 
remaining  the  same,  the  quantity  of  mixing  water  used  determines 
the  strength  of  the  concrete  as  long  as  the  mix  is  plastic.  Pro- 
fessor Abrams  found  that  the  compressive  strength  of  a  concrete 
made  with  a  certain  aggregate  depended  on  the  ratio  of  the 
volume  of  water  to  the  volume  of  cement  in  the  mix.  He  also 
found  that  there  was  a  close  relation  between  the  size  and  grading 
of  the  aggregate,  as  measured  by  its  fineness  modulus,  and  the 

1  NOTE. — Practically  all  of  this  article  is  taken,  with  Professor  Abrams' 
permission,  from  his  bulletin  on  the  "Design  of  Concrete  Mixtures"  pub- 
lished by  the  Structural  Materials  Research  Laboratory,  Lewis  Institute, 
Chicago. 


PLAIN  CONCRETE 


61 


amount  of  water  required  to  produce  mixes  of  uniform  plasticity 
or  consistency. 

The  fineness  modulus  is  a  term  used  to  denote  the  effective 
grading  of  an  aggregate.  It  is  computed  from  the  sieve  analysis 
of  the  aggregate.  For  making  the  sieve  analysis  the  following 


FIG.   18. — Abrams'  chart  for  the  design  of  concrete  mixers. 

Tyler  standard  sieves  are  used:  Nos.  100,  48,  28,  14,  8,  4;  and  % 
in.,  %  in.,  and  1^£  in-  Each  sieve  has  a  clear  opening  just 
double  that  of  the  preceding  one.  The  percentages  of  the  sample 
coarser  than  (held  on)  the  sieves  are  tabulated.  The  fineness 
modulus  of  the  aggregate  is  the  sum  of  the  percentages  divided  by 
100.  The  coarser  the  aggregate,  the  higher  the  fineness  modulus. 


62  MATERIALS  OF  CONSTRUCTION 

Results  of  tests  showed  that  mixtures  of  given  fine  and  coarse 
aggregates  having  the  same  fineness  modulus  and  the  same 
amounts  of  cement  and  water  produced  concretes  of  equal 
strength  (provided  that  the  concrete  was  plastic  and  the  aggre- 
gates were  not  too  coarse  for  the  amount  of  cement  used)  and 
of  equal  consistency.  Tests  also  showed  that  the  compressive 
strength  of  concrete  mixes  increased  with  the  fineness  modulus 
up  to  a  certain  value,  after  which  the  strength  decreased. 
This  point  of  maximum  strength  occurred  at  higher  values  of 
the  fineness  modulus  for  rich  mixes  than  for  lean  mixes. 

The  following  procedure  of  proportioning  by  fineness  modulus 
is  practically  the  same  as  that  proposed  by  Professor 
Abrams  : 

1.  Make  sieve  analysis  of  the  fine  and  the  coarse  aggregates, 
using  Tyler  standard  sieves  of  the  following  sizes:  Nos.  100,  48,  28, 
14,  8,  4;  and  %  in.,  %  in.,  and  1 J^  in.     Express  the  sieve  analysis 
in  terms  of  percentages  by  weight  of  material  coarser  than  each 
of  the  standard  sieves. 

2.  Compute  fineness  modulus  of  each  aggregate  by  adding  the 
percentages     obtained    in     the    sieve     analysis    and    dividing 
by  100. 

3.  Determine  the  maximum  size  of  the  aggregate  by  applying 
the  following  rules :     If  more  than  20  per  cent  of  the  aggregate  is 
coarser  than  any  sieve,  the  maximum  size  shall  be  taken  as  the 
next  larger  sieve  in  the  standard  set;  if  between  11  per  cent  and 
20  per  cent  is  coarser  than  any  sieve,  the  maximum  size  shall 
be  the  next  larger  "half  sieve;"  if  less  than  10  per  cent  is  coarser 
than  certain  sieves,  the  smallest  of  these  sieve   sizes  shall  be 
considered  the  maximum  size. 

4.  Assume  a  mix  and  from  Professor  Abrams'  table  determine 
the    maximum   size  of  fineness  modulus  which  may  be  used 
for  the   mix,  kind  and  size  of  aggregate,  and  the  work  under 
construction. 

5.  Compute  the  percentages  of  fine   and   coarse  aggregates 
required  to  produce  the  fineness  modulus  desired  for  the  final 

aggregate  by  applying  the  formula:  P  =  (\~^~r*\  ^® 

when  P  =  percentage  of  fine  aggregate  in  total  mixture. 
A  =  fineness  modulus  of  coarse  aggregate. 
B  =  fineness  modulus  of  final  aggregate  mixture. 
C  =  fineness  modulus  of  fine  aggregate. 


PLAIN  CONCRETE  63 

6.  Using  Professor  Abrams'  chart,  draw  a  straight  line  through 
the  mix  and  fineness  modulus  of  aggregate  used.     Note  where 
this  line  intersects  the  reference  line  of  consistency  (relative  con- 
sistency of  1.00).     Through  this  point  of  intersection  draw  a 
horizontal  line.     Read  the  strength  at  the  point  where  this 
horizontal  line  crosses  the  vertical  line  for  the  relative  consistency 
considered   in   design    (see  following   paragraphs  in   regard   to 
consistency). 

7.  If  the  mix  chosen  does  not  give  the  desired  strength,  select 
another  mix  and  try  again  until  a  suitable  mix  is  found. 

8.  Whenever  time  permits,  make  test  cylinders  of  the  mixes 
selected  and  test  them  at  age  of  28  days  for  a  check  on  the  design 
of  mix. 

The  use  of  Professor  Abrams'  chart  is  a  great  help  in  approxi- 
mately determining  the  mix  required  for  a  certain  compressive 
strength  when  the  relative  consistency  and  fineness  modulus 
are  known. 

The  relative  consistency  of  1.00  is  about  as  low  as  can  ever  be 
used,  and  this  consistency  requires  tamping.  For  ordinary 
plain  concrete  work,  a  relative  consistency  of  about  1.10  is  as 
low  as  should  be  used  for  designing.  For  ordinary  reinforced 
concrete  work,  a  relative  consistency  of  about  1.20  is  advised 
for  use  in  designing. 

In  making  concrete  the  least  amount  of  mixing  water  that 
will  produce  a  mix  of  workable  consistency  should  always  be 
used. 

The  compressive  strength  values  given  in  Professor  Abrams' 
chart  were  determined  from  compression  tests  on  6  by  12-in. 
cylinders  stored  in  a  damp  place  and  tested  at  an  age'  of  28  days. 
The  values  obtained  in  practical  work  will  probably  be  lower  than 
these  because  of:  less  care  used  in  mixing,  handling,  and  placing 
of  concrete;  variations  in  quality  of  cement;  variations  in  con- 
sistency; different  storage  or  curing  conditions:  and  variations 
in  age. 

Consequently,  whenever  practicable,  test  cylinders  should  be 
made  and  stored  under  conditions  similar  to  that  prevailing  on 
the  work  and  then  tested  at  an  age  of  28  days  as  a  check  on  the 
design  of  the  mix. 


64  MATERIALS  OF  CONSTRUCTION 

MAXIMUM  PRACTICAL  VALUES  OF  FINENESS  MODULUS  (ABRAMS) 


Properties  by  volume 

Aggregate:  Cement 

Size  mix  of 

aggregate 

2 

3 

4 

5 

6 

7 

9 

Mortars 

0-14 

3.00 

2.70 

2.50 

2.30 

2.15 

2.05 

1.95 

1.85 

0-  8 

3.80 

3.40 

3.10 

2.90 

2.75 

2.65 

2.55      2.45 

0-  4 

4.75 

4.20 

3.90 

3.60 

3.45 

3.30 

3.20 

3.05 

Concretes 

0-% 

5.60 

5.05 

4.70 

4.40 

4.20 

4.05 

3.95 

3.85 

0-K* 

6.05 

5.45 

5.10 

4.80 

4.60 

4.45 

4.35 

4.25 

0-M 

6.50 

5.90 

5.50 

5.20 

5.00 

4.85 

4.75 

4.65 

0-1* 

6.90 

6.30 

5.90 

5.60 

5.40 

5.25 

5.15 

5.00 

o-i  M 

7.35 

6.70 

6.30 

6.00 

5.80 

5.65 

5.55 

5  .  40 

0-2* 

7.75 

7.10 

6.70 

6.40 

6.20 

6.05 

5.95 

5.80 

0-3 

8.20 

7.55 

7.15 

6.85 

6.60 

6.50 

6.40 

6.25 

*  Half  sieves  not  used  in  computing  fineness  modulus. 

For  mixes  other  than  those  given  in  the  table,  use  the  values  for  the  next 
leaner  mix. 

For  maximum  sizes  of  aggregate  other  than  those  given  in  the  table,  use 
the  values  for  the  next  smaller  size. 

This  table  is  based  on  the  requirements  for  sand-and-pebble  or  gravel 
aggregate,  composed  of  .approximately  spherical  particles,  in  ordinary  uses 
of  concrete  in  reinforced  concrete  structures.  For  other  materials  and  in 
other  classes  of  work,  the  maximum  permissible  values  of  fineness  modulus 
for  an  aggregate  of  a  given  size  is  subject  to  the  following  corrections: 

1.  If  crushed  stone  or  slag  is  used  as  coarse  aggregate,  reduce  values  in 
table  by  0.25.     For  crushed  material  consisting  of  unusually  flat  or  elongated 
particles,  reduce  values  by  0.40. 

2.  For  pebbles  consisting  of  flat  particles,  reduce  values  by  0.25. 

3.  If  stone  screenings  are  used  as  fine  aggregate,  reduce  values  by  0.25. 

4.  For  the  top  course  in  concrete  roads,  or  other  work  requiring  a  smooth 
finish,  reduce  the  values  by  0.25.     If  finishing  is  done  by  mechanical  means, 
this  reduction  need  not  be  made. 

5.  In  work  of  massive  proportions,  such  that  the  smallest  dimension  is 
larger  than  10  times  the  maximum  size  of  the  coarse  aggregate,  additions 
may  be  made  to  the  values  in  the  table  as  follows:  for  %-in.  aggregate, 
0.10;  for  l^-in.,  0.20;  for  3-in.,  0.30;  for  6-in.,  0.40. 

Sands  with  fineness  modulus  lower  than  1.50  are  undesirable  as  fine 
aggregate  in  ordinary  concrete  mixes.  Natural  sands  of  such  fineness  are 
seldom  found. 

Sand  or  screenings  used  for  fine  aggregate  in  concrete  must  not  have  a 
higher  fineness  modulus  than  that  permitted  for  mortars  of  the  same  mix. 
Mortar  mixes  are  covered  by  the  table  and  by  (3)  above. 

Crushed  stone  mixed  with  both  finer  sand  and  coarser  pebbles  requires 
no  reduction  in  fineness  modulus,  provided  the  quantity  of  crushed  stone  is 
less  than  30  per  cent  of  the  total  volume  of  the  aggregate. 


PLAIN  CONCRETE  65 

77.  Proportioning  Concrete  by  Edwards'  Surface  Area  Method. 
This  method  is  one  proposed  by  Mr.  L.  N.  Edwards.    From 

the  results  of  tests  Mr.  Edwards  found  that,  with  aggregates  of 
uniform  quality,  the  strength  of  the  mortar  or  concrete  depended 
on  (1)  the  amount  of  cement  used  in  relation  to  surface  area  of 
the  aggregate,  and  (2)  the  consistency  of  the  mix.  He  also 
found  that,  other  things  being  equal,  the  fine  aggregate  with  a 
small  total  surface  area  gave  a  mortar  of  greater  strength  than  a 
like  aggregate  having  a  greater  surface  area.  Also  that  the 
amount  of  water  required  to  produce  a  mortar  of  normal  con- 
sistency depends  on  the  amount  of  cement  used  and  the  total 
surface  area  of  the  fine  aggregate  wetted. 

The  general  method  of  procedure  for  proportioning  concrete 
by  this  method  is  as  follows: 

1.  Make  a  sieve  analysis  of  the  aggregate. 

2.  Find  average  number  of  particles  per  unit  weight  of  the  aggregate 
passing  one  sieve  and  held  on  another. 

3.  From  the  results  of  (2)  and  the  specific  gravity  of  the  particles,  com- 
pute the  average  volume  of  each  size  of  particle. 

4.  Compute  the  surface  areas  from  the  average  volumes  of  the  various 
sizes  and  shapes  of  the  particles.     (Grains  of  sand  and  gravel  were  assumed 
as  spherical,  while  particles  of  broken  stone  were  assumed  to  be  one-third 
cubes  and  two-thirds  parallelepipeds.) 

5.  Determine  the  total  surface  area  of  the  aggregate. 

6.  Base  the  quantity  of  cement  on  the  total  surface  area. 

7.  Base  the  quantity  of  water  on  the  quantity  of  cement  and  the  total 
surface  area  of  the  aggregate. 

8.  Make  strength  tests  on  the  mortar  or  concrete  as  determined  in  (7). 

9.  Increase  or  decrease  the  cement  and  water  content  of  the  mix  until  a 
mix  is  found  that  gives  the  strength  required. 

The  proper  water-cement  ratio  must  always  be  maintained  or 
else  the  strength  results  will  not  be  satisfactory. 

The  work  required  for  this  method  of  proportioning  can  be 
simplified  in  the  laboratory  by  the  use  of  curves  and  tables 
showing  relations  between  surface  areas  and  unit  weights  of 
particles  of  various  sizes  and  specific  gravities,  water-cement 
ratios,  relations  between  strength  and  cement  content  and 
surface  areas,  etc. 

78.  Formula  for  Estimating  Quantities  of  Materials  Required 
for  Plain  Concrete. — The  following  formula  is  of  use  in  determin- 
ing the  quantities  of  cement,  fine  and  coarse  aggregates  required 
for  a  certain  volume  of  concrete.     The  units  may  be  any  con- 
venient units  of  volume,  provided  that,  in  any  one  problem,  the 

5 


66  MATERIALS  OF  CONSTRUCTION 

units  of  the  concrete,  cement,  fine  and  coarse  aggregates  are  the 
same.  Customary  units  are  cubic  feet  or  cubic  yards  (and  often 
barrels  for  the  cement). 

1    55  V^  C 

The  number  of  parts  of  cement  required  are  pr~     a    ,    ^  • 

U  +  b  +  ±t 

The  number  of  parts  of  fine  aggregate   (sand)   required  are 
1 .  55  X  S 

C  +  S  +  R' 

The  number  of  parts  of  coarse  aggregate  (stone)  required  are 
1 .  55  X  R 

C  +  S  +  R' 

C,  S,  and  R  are  the  proportions  of  cement,  sand,  and  stone, 
respectively,  in  the  mixture.  The  proportions  are  by  volume. 

The  number  of  parts  of  a  material  obtained  from  the  formula 
must  be  multiplied  by  the  volume  of  the  concrete  to  obtain  the 
volume  of  the  material  required.  If  the  volume  of  the  concrete 
is  in  cubic  feet,  the  volumes  of  the  cement,  sand,  and  stone  will 
be  in  cubic  feet  also. 

To  reduce  cubic  feet  of  cement  to  barrels,  divide  by  4  (assuming 
4  cu.  ft.  per  barrel).  Some  authorities  assume  3.8  cu.  ft.  per 
barrel  and  use  3.8  as  a  divisor  instead  of  4. 

To  reduce  cubic  feet  of  sand  or  stone  to  cubic  yards,  divide  by 
27,  there  being  27  cu.  ft.  in  1  cu.  yd. 

When  the  volume  of  concrete  is  small  enough  to  be  made  in  one 
batch,  it  is  customary  to  increase  slightly  the  quantities  of 
materials  required  to  allow  for  waste  due  to  the  concrete  sticking 
to  the  mixing  boards,  machines,  barrows,  tools,  etc.  This  in- 
crease in  the  quantities  is  usually  about  5  or  10  per  cent. 

C.  MIXING  OF  CONCRETE 

79.  Hand  Mixing. — As  the  strength  of  concrete  depends  to  a 
large  extent  upon  the  thoroughness  of  mixing,  great  care  should 
be  taken  in  mixing.  The  mixing  should  be  done"  on  water- 
tight platforms  of  sufficient  size  to  accommodate  the  men  and 
materials  for  the  progressive  and  rapid  mixing  of  at  least  two 
batches  of  concrete.  These  batches  should  be  small,  not  exceed- 
ing 1  cu.  yd. 

The  sand  should  be  evenly  spread  upon  the  platform  and  the 
cement  on  top  of  the  sand.  The  cement  and  sand  should  then 
be  mixed  dry  until  the  mixture  is  of  a  uniform  color.  Enough 
water  should  be  added  to  make  a  thin  mortar,  and  the  materials 


PLAIN  CONCRETE 


67 


FIG.  19. — Concrete  mixer.     (Koehring  Machine  Co.) 


FIG.  19o. — Concrete  mixer. 


68  MATERIALS  OF  CONSTRUCTION 

mixed  again.  Then  the  coarse  aggregate,  which  has  been  thor- 
oughly wetted,  should  be  placed  on  top  of  the  mortar  and  the 
whole  batch  thoroughly  mixed  until  it  is  of  a  uniform  consistency. 
More  water  may  be  added,  if  necessary,  so  that  the  batch  will  be 
of  the  desired  consistency.  From  three  to  five  turns  are  required 
at  each  stage  of  the  mixing. 

Some  engineers  prefer  to  mix  the  cement,  sand,  and  stone  dry 
and  then  add  the  water,  and  thoroughly  mix  again. 

80.  Machine  Mixing. — Machine  mixing  is  usually  much  better 
and  quicker  than  hand  mixing  and  should  generally  be  required 
when  the  amount  of  work  is  enough  to  make  machine  mixing 
economical.     In  machine  mixing  all  of  the  materials  (including 
the  water)  are  usually  introduced  at  once  without  any  inter- 
mediate mixing.     However,  some  authorities  think  that  better 
results  will  be  obtained  by  first  mixing  the  dry  materials  and  then 
adding  the  water  and  mixing  again.     The  time  required  for  mix- 
ing depends  upon  the  type  and  speed  of  the  mixer,  and  varies  for 
different  machines.     For  the  best  results,  the  time  of  mixing 
should  rarely  be  less  than  1  minute  after  the  water  is  added. 
Machine   mixed   concrete  is   often   stronger  than  hand  mixed 
concrete. 

Machine  mixers  are  of  two  kinds,  the  batch  and  the  continuous 
type.  In  a  batch  mixer,  the  proper  amounts  of  materials  for  one 
batch  are  added  and  mixed  and  discharged  from  the  mixer,  and 
then  the  operation  is  repeated  again.  The  mixing  is  done  by 
moving  paddles  or  blades  or  by  the  rotation  of  the  receptacle 
itself.  The  batch  mixer  usually  consists  of  a  fixed  or  revolving 
drum  with  movable  or  fixed  paddles  or  blades  inside.  In  a 
continuous  mixer  the  operation  of  mixing  is  practically  continu- 
ous, care  being  taken  to  maintain  the  proper  proportions  of  the 
materials.  These  mixers  usually  consist  of  a  trough  containing 
some  form  of  screws  or  paddle  wheels  to  assist  in  the  mixing. 
The  batch  mixer  gives  better  results  because  it  is  easier  to  super- 
vise the  operations  and  also  to  secure  the  proper  proportions  of 
the  materials  in  the  concrete. 

81.  Consistency    of    Concrete. — At    the    present    time    most 
engineers  favor  a  consistency  where  just  enough  water  has  been 
used  so  that  the  concrete  will  just  flow.     This  consistency  gives 
a  concrete  that  can  be  deposited  by  means  of  spouts  and  pipes  and 
which  requires  but  little  puddling  or  tamping  in  the  forms  to  make 
it  homogeneous  and  to  secure  smooth  surfaces  next  to  the  forms. 


PLAIN  CONCRETE  69 

A  consistency  that  requires  tamping  to  make  the  concrete 
quake  is  usually  better,  stronger,  and  more  impervious  than  the 
above  consistency,  but  it  is  not  quite  so  economical  in  placing 
and  tamping. 

A  very  wet  concrete  contains  more  voids  and  is  weaker  than  the 
above  concretes  and,  if  it  is  not  quickly  placed,  there  is  a  tendency 
for  the  materials  to  segregate. 

A  dry  concrete  requires  much  tamping  and  very  careful  inspec- 
tion in  order  to  secure  good  work. 

D.  DEPOSITION  OF  CONCRETE 

82.  Forms  for  Concrete. — In  general,  the  forms  used  for  con- 
crete should  be  durable  and  rigid  and  well  braced  to  prevent  any 
bulging  or  twisting,  as  well  as  strong  and  tight  enough  to  prevent 
leakage  of  the  concrete. 

The  forms  for  concrete  are  usually  constructed  out  of  cheap 
rough  lumber,  such  as  rough  pine  or  spruce,  using  the  better 
grades  of  lumber  only  when  a  very  smooth  concrete  surface  is 
desired.  Green  lumber  is  better  than  dry  because  it  will  not  be 
affected  by  the  water  in  the  concrete  to  so  large  an  extent.  The 
forms  should  be  constructed  so  that,  after  the  concrete  has 
hardened,  they  can  be  readily  removed  without  much  damage  to 
the  lumber.  Lumber  for  ordinary  forms  can  be  used  from  three 
to  five  times  on  an  average  before  it  is  damaged  enough  to  be 
thrown  away. 

Sometimes  metal  forms  are  used.  There  are  a  number  of 
types  of  these  forms  on  the  market.  A  good  metal  form  can  be 
used  very  many  times  before  it  becomes  worn  out.  Conse- 
quently, metal  forms  are  economical  when  the  amount  of  work 
will  admit  of  their  repeated  use,  even  though  their  first  cost  is 
greater  than  that  of  wooden  forms. 

83.  Transporting,  Placing,  and  Tamping  Concrete. — In  general, 
the  transportation  system  must  be  such  that  the  concrete  will  be 
carried  from  the  mixer  to  the  forms  before  it  attains  initial  set; 
that  no  part  of  the  concrete  will  be  lost  in  transporting;  that  no 
segregation  of  materials  will  take  place;  that  the  delivery  of  the 
concrete  will  be  continuous  and  uninterrupted;  and  that  the 
transporting  will  be  done  efficiently,  rapidly,  and  economically. 
Some  of  the  methods  of  transportation  are  shovels,  wheelbarrows, 
carts,  large  buckets,  cableways,  pipes,  spouts,  spouting  plants 


70  MATERIALS  OF  CONSTRUCTION 

(including  hoists,  dump  buckets,  concrete  bins,  pipes,  and 
spouts),  etc. 

In  placing  concrete  care  should  be  taken  to  see  that  the  concrete 
shall  be  continuously  and  evenly  placed;  segregation  avoided; 
laitance  and  stoppage  planes  prevented;  voids  reduced;  and 
lateral  flow  prevented.  Also  that  concrete,  that  has  been  re- 
mixed after  initial  set  has  taken  place,  should  not  be  placed  in 
the  forms.  Extra  care  is  required  in  depositing  concrete  in  cold 
or  very  hot  weather.  Usually,  the  concrete  is  placed  in  the  forms 
in  layers  about  6  or  8  in.  deep  and  a  new  layer  added  before  the 
other  has  set. 

All  concrete  should  be  puddled  or  tamped  when  it  is  placed  in 
the  forms  to  eliminate  voids,  bring  any  free  water  to  the  surface, 
secure  a  close  filling  of  the  forms  and  contact  with  the  reinforce- 
ment, make  the  concrete  more  homogeneous,  and  make  a  dense 
mortar  coat  and  smooth  finish  at  the  exterior  surfaces. 

After  placing  the  concrete,  care  should  be  taken  to  prevent 
a  too  rapid  drying.  It  should  be  kept  moist  for  at  least  2  weeks 
after  the  removal  of  the  forms. 

84.  Bonding  New  Concrete  to  Old  Work. — In  joining  fresh 
concrete  to  hardened  concrete  or  to  old  masonry,  the  surface  of 
contact  should  be  thoroughly  cleaned  of  all  loose  material,  dirt, 
and  laitance  before  depositing  the  fresh  concrete.     If  a  strong 
bond  is  desired,  the  surface  should  be  washed  with  a  dilute  acid 
solution  and  water  and  then  plastered  with  a  coat  of  rich  cement 
mortar  or  grout.     If  necessary,  the  contact  surface  should  be 
roughened  with  tools,  as  a  good  bond  can  be  more  easily  secured 
on  a  rough  surface. 

A  cement  grout  is  a  very  thin  and,  usually,  rich  mortar. 

Laitance  is  a  whitish,  chalky  substance  washed  out  of  the 
cement  in  the  concrete.  This  substance  appears  on  the  surface 
of  practically  all  concretes,  has  little  or  no  strength  and  hardening 
properties,  weakens  the  bond  between  old  and  new  concrete,  and 
spoils  the  appearance  of  the  structure.  It  may  be  removed  by 
scrubbing. 

85.  Surface  Finish  of  Concrete. — As  the  surface  of  concrete 
often  shows  the  marks  of  the  forms  after  their  removal,  it  is  some- 
times necessary  to  finish  the  surface  to  improve  its  appearance. 

One  method  is  to  finish  the  surface  by  tooling.  The  use  of 
different  tools  (chisels,  hammers,  etc.)  will  give  a  variety  of 
finished  surfaces.  Changing  the  angle  at  which  the  chisel  is 
held  will  also  change  the  appearance  of  the  surface. 


PLAIN  CONCRETE  71 

Another  method  is  to  give  the  surface  a  rub  finish  by  rubbing  it 
with  carborundum  stone,  emery,  concrete,  or  a  soft  natural  stone. 
This  type  of  finish  is  not  expensive  and  gives  a  good  surface. 

Sometimes  the  forms  covering  the  exposed  surfaces  are  removed 
and  the  concrete  surface  brushed  while  the  concrete  is  still  green. 
A  wire  brush  is  usually  used. 

Sandblasting  is  sometimes  used  to  finish  a  concrete  surface  that 
is  thoroughly  hardened.  Care  should  be  taken  not  to  make 
depressions  in  the  surface  or  to  round  off  the  edges  too  much. 

A  very  pleasing  finish  is  secured  by  the  use  of  colored  aggregates 
in  the  concrete  and  then  properly  finishing  the  surfaces. 

White  cement,  pigments,  and  stains,  etc.  are  often  used  to 
secure  desired  surface  finishes. 

Plaster  coatings  should  rarely  ever  be  applied  to  concrete 
surfaces  as  they  are  generally  not  durable. 

86.  Placing  Concrete  Under  Water. — Concrete  may  be  placed 
under  water  if  there  is  little  or  no  current  flowing,  as  a  current  of 
water  tends  to  wash  the  cement  out  of  the  concrete  before  it 
can  harden. 

Probably  the  best  way  of  placing  concrete  under  water  is  by 
using  a  metal,  tube  (called  a  "tremie")  about  1  ft.  in  diameter, 
slightly  flaring  at  the  bottom,  and  long  enough  to  reach  from  the 
bottom  to  above  the  surface  of  the  water.  The  tube  should  be 
kept  full  of  concrete  all  the  time,  and  the  bottom  of  the  tube 
should  be  moved  about  slowly  so  as  to  allow  of  the  gradual 
discharge  of  the  concrete. 

Another  method  is  to  deposit  the  concrete  in  large  quantities  in 
fairly  tight  molds  and  then  not  disturb  it  before  it  attains  its 
final  set. 

Bottom  dumping  buckets  fitted  with  top  covers  have  been  used 
more  or  less  successfully  in  some  places. 

Sometimes  the  concrete  is  placed  in  bags  of  loosely  woven 
cloth,  jute,  or  burlap  and  then  deposited  under  the  water,. 

87.  Placing   Concrete   in  Freezing  Weather. — If  it'  can   be 
avoided,   concrete  should  not  be  placed  in  freezing  weather. 
However,  fairly  good  work  may  be  done  if  proper  precautions 
are  taken  to  keep  the  concrete  from  freezing  before  it  sets.     This 
may  be  accomplished  in  various  ways  such  as  heating  the  forms 
by  steam  pipes,  by  adding  salt  to  the  mixing  water,  by  heating 
the   materials   before   mixing  and   placing  them,   or  by  some 
combination  of  these  methods.     If  salt  is  added  to  the  mixing 


72  MATERIALS  OF  CONSTRUCTION 

water,  it  requires  about  1  per  cent  of  salt  by  weight  to  reduce  the 
freezing  temperature  of  the  concrete  1  degree  Fahrenheit. 
More  than  8  or  10  per  cent  of  salt  should  never  be  used  (except 
in  extreme  cases)  as  it  may  seriously  lower  the  strength  of  the 
concrete.  Calcium  chloride  has  less  effect  on  the  strength  of  the 
concrete  than  the  ordinary  sodium  chloride  has.  Also,  calcium 
chloride  accelerates,  while  sodium  chloride  retards,  the  setting  of 
the  concrete. 

Alternate  freezing  and  thawing  of  concrete  have  a  bad  effect  on 
the  strength  and  should  be  very  carefully  guarded  against.  The 
freezing  of  concrete  after  the  final  set  has  taken  place  does  but 
very  little  damage  to  it. 


E.  IMPERVIOUS  CONCRETE 

88.  Impervious  Concrete  in  General. — While  it  is  impossible 
to  make  concrete  actually  waterproof,  it  may  be  made  practically 
impervious  by  several  different  methods  or  combinations  of  these 
methods.     Though  it  is  practically  impossible  to  keep  out  all  of 
the  water,  yet  the  water  may  be  prevented  from  passing  through 
the  concrete  in  such  amounts  as  to  cause  inconvenience  and 
damage.     In  general,  the  flow  of  water  through  the   concrete 
varies  directly  with  the  amount  of  voids  in  the  concrete  (the 
voids  may  be  large,  due  to  imperfect  grading  of  the  aggregates, 
excess   of   mixing   water,    improper   mixing,   improper   placing, 
segregation  of  materials,  etc.),  the  water  pressure  or  head  on  the 
concrete,  the  amount  of  laitance,  and  the  number  of  shrinkage  or 
temperature  cracks.     The  flow  of  water  through  the  concrete 
varies  inversely  with  the  age,  the  density,  and  the  amount  of 
cement. 

89.  Effect  of  Increasing  the  Density  and  Amount  of  Cement. — 
Concrete  may  be  made  more  water-tight  by  making  it  more  dense, 
but  this  requires  great  care  in  the  proportioning,  mixing,  and 
placing.     The  more  dense  the  concrete,  the  more  impervious  it  is. 
Greater  density   may  be  secured  by  a  proper  grading  of  the 
materials  so  as  to  secure  a  minimum  percentage  of  voids.     An 
excess  of  mixing  water  must  be  avoided,  as  this  excess  will  form 
water  voids.     Also,  too  little  water  must  not  be  used  as  a  dry 
concrete  is  not  so  impervious  as  a  slightly  wet  mix.     A  concrete 
made    by    using  a  slightly    wet   consistency  with  well-graded 


PLAIN  CONCRETE  73 

aggregates  and  which  is  thoroughly  puddled  in  the  molds  will 
give  a  fairly  water-tight  structure.  Care  must  be  taken  to 
prevent  cracks. 

Increasing  the  amount  of  cement  used  tends  to  make  the  con- 
crete more  water-tight.  The  richer  the  mix,  the  better  it  is.  A 
concrete  leaner  than  a  1:6  should  not  be  used. 

Increasing  the  density  and  the  amount  of  cement  are  the  best 
methods  in  use  at  present  for  increasing  the  water-tightness  of 
concrete. 

90.  Using  Waterproofing  Materials. — Concrete  may  be  made 
practically   water-tight   by   placing   layers   of   a   waterproofing 
material  between  layers  of  the  concrete,  but  great  care  must  be 
taken  in  order  to  secure  a  good  bond  between  these  layers. 
Sometimes  a  layer  of  asphalt  is  placed  between  two  layers  of 
concrete.     Often  a  tar  paper  or  a  roofing  felt  is  placed  between 
concrete  layers  and  bonded  to  them  by  a  coating  of  hot  asphalt  or 
tar.     Frequently   several   layers   are  used.     Continuity  of  the 
paper  or  felt  is  important 

91.  Using  Foreign  Matter  in  the  Concrete. — An  addition  of 
from  8  to  15  per  cent  of  hydrated  lime  (based  on  the  weight  of 
the  cement)  to  the  concrete  aids  in  reducing  the  porosity  and 
thus  making  the  concrete  more  water-tight.     Other  materials 
such  as  fireclay,  feldspar,  ground  sand,  etc.  have  been  used  for 
the  same  purpose  with  varying  success. 

Sometimes  small  percentages  (2  or  3  per  cent)  of  an  alum  soap 
solution  (1  part  alum  to  2.2  parts  soap),  chloride  of  lime,  oil 
emulsions,  and  similar  compounds  have  been  used  to  make  the 
concrete  more  impervious  by  acting  as  a  void  filler  and  a  water 
repellant.  As  most  of  these  compounds  tend  to  weaken  the 
concrete  large  percentages  should  not  be  used. 

92.  Use  of  Surface  Treatments. — In  order  to  make  the  con- 
crete more  impervious,  the  surface  may  be  given  one  or  more 
coats  of  oil  paint,  varnish,  bitumen  (asphalt,    petroleum,  coal 
tar,  etc.),  a  paraffin  solution  in  benzine  or  benzol,  soap,  soap  and 
alum,   cement  grout,   or   cement  mixed  with  a  waterproofing 
material.     A  plastering  with  a  rich  cement  mortar  is  effective, 
provided  a  good  bond  can  be  secured  and  cracks  can  be  prevented 
from  forming.     Surface  treatments  aid  in  making  existing  struc- 
tures more  water-tight. 


74  MATERIALS  OF  CONSTRUCTION 

F.  PROPERTIES  OF  CONCRETE 

93.  Effect  of  Various  Impurities  Mixed  with  the  Concrete.— 

Mica. — A  very  small  amount  of  mica  in  concrete  will  cause  an 
appreciable  loss  of  strength. 

Dirt. — An  appreciable  amount  of  dirt  is  apt  to  have  an  in- 
jurious effect  on  the  strength  of  concrete. 

Organic  Matter. — All  organic  matter  should  be  carefully 
excluded  from  concrete.  As  small  an  amount  as  Mo  of  1  per 
cent  may  be  injurious. 

Clay. — A  small  amount  of  clay  is  sometimes  beneficial,  espe- 
cially in  lean  mixes,  but  a  large  amount  (over  10  per  cent)  will 
weaken  the  concrete.  A  concrete  that  has  a  large  percentage  of 
voids  may  be  improved  by  the  addition  of  a  small  amount  of 
finely  divided  clay. 

Loam. — Loam  has  about  the  same  effect  as  clay. 

Lime. — Unhydrated  (quicklime)  lime  should  never  be  placed 
in  concrete  as  the  expansion  during  the  hydration  will  probably 
cause  the  disintegration  of  the  concrete.  Hydrated  lime  has 
about  the  same  effect  as  clay.  Small  percentages  of  hydrated 
lime  often  improve  porous  or  lean  concretes  but  are  usually 
injurious  to  rich  or  dense  concretes.  In  general,  hydrated  lime 
is  preferable  to  clay. 

Sugar. — A  very  small  percentage  of  sugar  has  a  bad  effect  on 
the  strength  and  soundness  of  concrete. 

Grease  and  Oil. — These  materials  have  an  injurious  effect  on 
the  concrete  when  mixed  with  the  concrete  materials  in  the 
making  of  the  concrete. 

Regaging. — Regaging,  retempering,  or  remixing  a  portland 
cement  concrete  is  generally  not  permitted  as  it  is  thought  to 
be  very  injurious  to  the  concrete.  Concrete  that  has  passed 
the  stage  of  initial  set  should  never  be  placed  in  the  forms. 

94.  Effect  of  Various  Elements  on  Hardened  Concrete. — Fire. 
Concrete  has  better  fire-resisting  qualities  than  ordinary  brick, 
stone,  tile,  or  terra  cotta.     Concrete  may  be  heated  to  1,200 
degrees  Fahrenheit  (this  is  as  hot  as  an  ordinary  fire)  for  3  or 
4  hours  and  then  suddenly  cooled  with  a  stream  from  a  fire 
hose  without  showing  more  than  a  slight  surface  disintegration. 
A  thickness  of  about  2  in.  of  concrete  over  steel  is  enough  to 
keep  the  steel  from  warping,  bending,  twisting,  or  being  other- 
wise damaged  in  an  ordinary  building  fire.     Of  course,  aggregates 
which  will  ignite  or  disintegrate  at  comparatively  low  tempera- 


PLAIN  CONCRETE  75 

tures  (less  than  1_,700  degrees  Fahrenheit)  should  not  be  per- 
mitted in  a  concrete  that  may  be  subjected  to  fire. 
.  Acids. — A  thoroughly  hardened  concrete  of  first-class  quality 
is  affected  only  by  strong  acids  such  as  would  seriously  injure 
other  materials. 

Grease  and  Oil. — A  concrete,  properly  made  and  hardened, 
and  with  a  carefully  finished  surface,  will  resist  the  action  of 
ordinary  engine  oils  and  petroleum. 

Sea  Water. — Sea  water  has  practically  no  effect  on  good  con- 
crete made  with  properly  manufactured  cement  and  good 
aggregates  and  containing  a  very  small  percentage  of  voids. 
Some  concrete  structures  exposed  to  sea  water  have  been  seri- 
ously disintegrated.  This  action  usually  occurs  at  the  water 
line  and  may  be  shown  by  a  swelling  and  cracking  of  the  concrete, 
a  softening  and  crumbling  of  the  mortar,  or  a  formation  of  a 
crust  which  later  cracks  off.  The  disintegration  of  reinforced 
concrete  is  often  due  to  the  sea  water  penetrating  the  concrete 
and  causing  the  steel  to  rust.  In  most  cases  the  disintegration 
is  due  to  poor  cement,  poor  aggregates,  or  poor  proportioning, 
mixing,  or  placing  of  the  concrete.  A  rich  mortar  coat,  a  few 
inches  thick,  applied  to  the  concrete  at  the  water  line  tends  to 
protect  the  concrete  from  the  action  of  the  sea  water.  It  is 
thought  that  the  active  element  in  the  sea  water  is  sulphate  of 
magnesia. 

Alkali. — It  has  been  frequently  noted  that  concrete,  which  has 
been  partly  submerged  in  alkali  water,  often  disintegrates  near 
the  water  line*.  The  disintegration  is  like  that  of  concrete 
exposed  to  sea  water.  Just  what  chemical  action  takes  place  is 
not  known,  but  the  active  element  is  thought  to  be  sulphate  of 
magnesia.  Aggregates  which  contain  alkali  should  not  be  used 
in  concrete  work. 

95.  Effect  of  Varying  the  Amount  of  Mixing  Water. — Water 
has  four  functions  in  concrete;  i.e.,  (1)  to  react  with  the  cement 
and  form  a  binding  material;  (2)  to  aid  in  spreading  the  cement 
over  the  surfaces  of  the  aggregates;  (3)  to  act  as  a  lubricant 
between  the  particles  of  the  fine  and  the  coarse  aggregates  and 
thus  aid  in  the  placing  of  the  mixture  in  the  molds;  and  (4)  to 
occupy  space  in  the  concrete. 

There  should  be  enough  water  present  to  react  with  all  of  the 
cement.  If  too  little  water  is  used,  the  reaction  will  not  be 
complete;  while  if  too  much  water  is  used,  the  mixture  will  be 


76 


MATERIALS  OF  CONSTRUCTION 


too  dilute  to  develop  the  best  strength.  These  effects  are  shown 
by  strength  tests  on  concretes  of  dry,  normal,  and  wet  consist- 
encies. While  a  dry  mix  may  give  greater  strength  in  short  time 
tests,  the  normal  mix  is  nearly  always  the  stronger  after  a  few 
months  have  elapsed. 

Enough  water  should  be  present  to  carry  the  particles  of 
cement  and  spread  them  over  the  surfaces  of  the  particles  of  the 
aggregates.  Too  little  water  will  not  allow  of  the  proper  spread- 
ing of  the  cement  particles,  while  too  much  water  will  tend  to 
keep  the  cement  from  sticking  to  the  aggregates. 


90 

r 

i: 

\  Th/s  consistency  for  'mach'/ne 
\made  concrete  products. 
\j<?  pending  on  fvpe  ofmach/'ne-, 

\ 

// 

V 

r-Prc 
con 

perc 

on^h 

-tenc^ 

'  forr 

rjass  cone/ 

-ete. 

^ 

/ 

/ 
1 

1  |  |  ~~h=: 

hich  can  be  obta/ned 

^\ 

-Thi 

r  ra/?i 
fed  t 
-rete, 
great 

?e  oft 

'or  ca 
etc;t 
er  ar, 

'onsi. 
sf  f>r 
fyr?  m 

vduct^re/n 
?m  tiers  re 

M 

forcea 
fu/re 

V 

be  u 
com 

\the 

\ 

\ 

r-With  this  consists 
J  one-/?a/fthe  strt 

ncy  < 
ngf/? 

ibout 

* 

\ 

L 

^ 

1 

X 

^ 

to 

0 

>W/7  /-^(f  's/opf>\/'eoncrete  fome~^** 
%m-f?-    used  '  /h  road  work  and  in 
Duila/nq  constractionj  trfo-thirds 
to  three-fourths  of  the  possib/e 
strength  of  the  concrete  />  Josf- 

^r 

^ 

*—  »«^r 

i 

Oj 

tv       ov        vu        itiv       110       {20      /30       I4O      150       ICO      J7O       J£O      I3O      ZSO 

Water Used.-  F/gures  are  percent-  of  Quantify  (fit/ing  Max'/mum  Strength. 
FIG.  20. — Effect  of  quantity  of  mixing  water  on  strength  of  concrete.      (Abrams.) 

Too  little  water  retards  the  flowing  of  the  concrete  and  makes 
it  difficult  to  place  the  concrete  in  the  molds  and  compact  it 
properly,  while  too  much  water  tends  to  cause  segregation  of  the 
materials.  Enough  water  should  be  present  for  the  proper 
lubrication  of  the  materials  and  no  more. 

Water  occupies  space  in  the  concrete  and,  if  too  much  is  used, 
it  tends  to  push  the  solid  particles  farther  apart  and  make  the 
mixture  less  dense.  Further,  this  excess  of  water  may  escape, 
after  the  concrete  has  set,  and  leave  air  voids. 

Excess  of  water  also  has  the  following  bad  effects  on  concrete: 
(1)  it  tends  to  cause  day-work  planes;  (2)  it  tends  to  cause  large 
deposits  of  laitance;  (3)  it  makes  the  concrete  less  impervious; 
(4)  it  increases  the  difficulty  of  bonding  new  to  old  concrete; 


PLAIN  CONCRETE  77 

(5)  it    tends    to    make    dusty    concrete    floor    surfaces;  and 

(6)  it    increases    the    difficulties    of     concreting     in     freezing 
weather. 

It  is  very  important  that  just  the  proper  amount  of  water  be 
used  in  concrete  work  and  that  the  engineer  in  charge  of  the  work 
regulate  the  water  at  all  times  so  as  to  secure  the  proper  consist- 
ency. Different  cements  and  different  aggregates  (and  some- 
times different  batches  of  the  same  aggregates)  often  require 
slightly  varying  amounts  of  water  for  the  normal  consistency. 

96.  Strength  of  Concrete  in  General. — In  general,  the  strength 
of  a  Portland  cement  concrete  depends  upon:  (1)  the  amount  of 
cement  per  unit  volume ;  (2)  the  density  of  the  concrete ;  and  (3) 
in  some  cases  upon  the  strength  of  the  aggregates.  Of  course, 
the  strength  of  concrete  increases  with  its  age,  but  the  rate  of 
increase  decreases  with  the  age. 

Any  factors  which  influence  any  of  the  above  conditions  will 
also  affect  the  strength  of  the  concrete.  Some  of  these  factors 
are:  the  consistency;  the  conditions  of  mixing,  placing,  and 
storing  or  aging;  the  qualities  of  the  cement,  water,  fine  and 
coarse  aggregates;  presence  of  impurities;  etc. 

Results  of  tests  indicate  that  concretes  stored  or  aged  in  damp 
or  moist  air  are  stronger  than  those  aged  in  water  or  dry  air. 
Also,  that  concretes  exposed  to  the  weather  (sun,  wind,  and  rain) 
are  usually  stronger  than  concretes  cured  indoors  in  a  compara- 
tively dry  room. 

A  concrete  of  a  slightly  dry  consistency,  well  mixed  and 
thoroughly  tamped,  is  generally  stronger  than  a  concrete  of 
slightly  wet  consistency,  but  the  wetter  consistency  gives  better 
results  in  practical  work  and  is  necessary  in  reinforced  concrete 
work.  Also,  a  concrete  of  a  slightly  wet  consistency  becomes 
about  as  strong  as  the  dry  mix  at  the  age  of  6  months.  A  very 
wet  mix  or  a  very  dry  mix  never  becomes  so  strong  as  a  normal 
mix  and  should  not  be  used  if  it  can  be  avoided. 

With  good  grading,  the  actual  size  of  the  stone  has  but  little 
effect  on  the  strength  of  the  concrete.  Usually,  a  small  size  of 
stone  is  less  well  graded  and  gives  less  density  when  mixed  with 
the  sand.  For  plain  concrete,  the  maximum  size  of  the  stone 
should  rarely  be  less  than  1  in.  The  maximum  size  in  reinforced 
concrete  work  depends  upon  the  molds  and  the  spacing  of  the 
reinforcement. 

Tests  show  that  broken  stone   generally  makes   a  stronger 


78  MATERIALS  OF  CONSTRUCTION 

concrete  than  gravel,  though  this  difference  is  not  very  great 
(about  10  per  cent). 

The  strength  of  the  coarse  aggregate  may  have  an  effect  on  the 
strength  of  the  concrete  if  enough  cement  is  used  so  that  the 
failure  takes  place  in  the  aggregate.  Ordinary  stone  and  gravel 
have  enough  strength  for  most  kinds  of  concrete.  Soft,  friable 
stones,  such  as  some  of  the  sandstones,  will  give  a  weaker  con- 
crete. Cinders,  brick,  old  concrete,  etc.  should  be  carefully 
investigated  as  to  their  strength  before  being  used  in  concrete. 

The  presence  of  such  materials  as  will  reduce  the  strength  of 
neat  cement  and  cement  mortar  will  also  tend  to  reduce  the 
strength  of  the  concrete. 

97.  Compressive  Strength  of  Concrete. — The  compressive 
strength  of  concrete  depends  primarily  upon  the  amount  of 
cement  per  unit  volume  and  also  upon  other  conditions  such  as 
were  discussed  in  the  preceding  article. 

For  a  1:2:4  mix  of  concrete,  made  under  reasonably  good 
conditions  as  to  the  character  of  the  materials  and  workmanship, 
an  average  strength  of  2,000  Ib.  per  square  inch  may  be  expected 
at  the  age  of  1  or  2  months.  Under  similar  conditions,  a  1:3:6 
mix  should  average  about  1,600  Ib.  per  square  inch.  Poorer  or 
better  results  may  be  obtained,  depending  upon  the  quality  of 
the  materials  and  the  workmanship. 

An  average  of  25  cylinders,  each  10  in.  in  diameter  and  24  in. 
long,  of  a  1:2:4  mix  of  machine  made  concrete  tested  at  the 
University  of  Wisconsin  gave  an  average  strength  of  1,940  Ib. 
per  square  inch  at  an  age  of  30  days.  An  average  of  44  cylinders 
of  the  same  kind  gave  a  strength  of  2,150  Ib.  per  square  inch  at  an 
age  of  60  days.  A  fairly  fine  sand  was  used.  The  consistency 
of  the  concrete  was  soft,  and  the  specimens  were  stored  in  air 
and  kept  moist  by  sprinkling. 

The  following  table  gives  results  of  tests  made  on  12-in.  cubes 
at  the  Watertown  Arsenal.  Standard  Portland  cement,  a  clean 
coarse  sharp  sand,  and  crushed  stone  (having  a  maximum  size  of 
2J-2  in.  and  49.5  per  cent  of  voids)  were  used.  The  cubes  were 
buried  in  wet  ground  after  their  removal  from  the  molds. 

The  compressive  strength  of  concrete  increases  with  age,  reach- 
ing about  80  or  90  per  cent  of  its  ultimate  at  the  age  of  2  months. 

The  compressive  strength  of  a  good  cinder  concrete  is  about 
one-third  of  the  strength  of  a  corresponding  mix  of  a  good  stone 
concrete. 


PLAIN  CONCRETE  79 

COMPRESSIVE  STRENGTH  OF  TWELVE  INCH  CUBES  OF  CONCRETE 


Mix 

Strength  in  pounds  per  square  inch 

Age  7  days 

Age  1  month 

Age  3  months 

Age  6  months 

1:2:4 
1:3:6 

1,565 
1,311 

2,399 
2,164 

2,896 
2,522 

3,826 
3,088 

From  the  results  of  tests  it  has  been  observed  that  the  strength 
of  short  concrete  columns  (as  long  as  10  or  15  diameters)  is  from 
10  to  20  per  cent  less  than  that  of  short  concrete  prisms. 

98.  Tensile  Strength  of  Concrete. — Satisfactory  tensile  tests 
of  concrete  are  very  difficult  to  make.     The  tensile  strength 
varies  from  about  Ho  to  Jf  2  of  the  compressive  strength.     The 
quality  of  the  materials  and  the  workmanship  both  have  a  very 
great  effect  on  the  tensile  strength.     The  same  factors  that  affect 
the  compressive  strength  also  affect  the  tensile  strength.     The 
tensile  strength  of  a  well-made  concrete  at  an  age  of  60  days  is 
about  as  follows: 

1:2:4  mix  of  concrete 175  to  275  Ib.  per  square  inch 

1:3:6  mix  of  concrete 125  to  200  Ib.  per  square  inch 

99.  Transverse  Strength  of  Concrete. — The  transverse  strength 
of  concrete  depends  upon  the  tensile  strength.     The  computed 
modulus  of  rupture  is  about  twice  the  tensile  strength  and  from 
J£  to  %  of  the  compressive  strength.     The  following  table  gives 
an  idea  of  the  cross-bending  strength  of  good  concrete  of  various 
mixes  at  an  age  of  one  month: 

TRANSVERSE  STRENGTH  OF  CONCRETE  (ON  TENSION  SIDE)  1  MONTH  OLD 


Modulus  of 

Modulus  of 

Mix  of  concrete 

rupture,  pounds 
per  square  inch 

Mix  of  concrete 

rupture,  pounds 
per  square  inch 

1:1^:3 
1:2:4 

475 
425 

1:3:5 
1:3:6 

275 
225 

1:2:5 

350 

1:4:8 

125 

80 


MATERIALS  OF  CONSTRUCTION 


100.  Shearing  Strength  of  Concrete.— The  shearing  strength 
of  concrete  is  of  importance  especially  in  short  concrete  columns 
and  reinforced  beams.  Satisfactory  shearing  tests  on  concretes 
are  hard  to  make,  due  to  the  difficulty  of  securing  apparatus 
that  will  give  a  pure  shearing  stress.  The  shearing  strength  of 
concrete  usually  varies  from  J^  to  %  of  the  compressive  strength. 
Tests  on  concrete  at  the  University  of  Illinois  gave  the  following 
results.  The  shear  specimens  were  restrained  beams  and  the 
compression  specimens  were  cubes.  The  specimens  were 
stored  in  damp  sand. 


Mixture 

Shear, 
pounds  per 
square  inch 

Compression, 
pounds  per 
square  inch 

Comp. 
Ratio-- 
Shear 

.    Shear 
Ratio 

Comp. 

1:2:4 

1,418 

3,210 

2.26 

0.44 

1:3:6 

1,313 

2,428 

1.85 

0.54 

1:3:6 

1,020 

1,721 

1.69 

0.59 

101.  Adhesive  Strength  of  Concrete  to  Steel.— The  adhesive 
strength  (or  bond)  of  concrete  to  steel  is  of  great  importance 
in  reinforced  concrete  work.  This  strength  depends  upon  the 
richness  of  the  mix  and  on  the  character  of  the  surface  of  the  steel. 
Corrugated  rods  usually  give  greater  bond  stresses  than  plain 
rods.  Bond  tests  have  been  made  in  two  different  ways.  One 
way  was  to  measure  the  force  required  to  pull  a  rod  out  of  a  block 
of  concrete  (pull  out  test) ,  and  the  other  method  was  to  determine 
the  force  required  to  make  a  rod  slip  in  a  beam.  The  tests 
showed  that  the  bond  between  the  concrete  and  steel  was  divided 
into  two  parts;  the  adhesion  between  the  concrete  and  steel  and 
the  sliding  resistance.  The  adhesive  strength  may  be  said  to 
have  been  reached  when  the  first  end  slip  of  the  rod  was  observed. 
This  stress  is  about  %  or  %  the  maximum  stress  attained.  The 
beam  tests  are  thought  to  have  given  more  reliable  values 
than  the  pull  out  tests.  Results  of  beam  tests  gave  maximum 
bond  stresses  varying  from  160  to  375  Ib.  per  square  inch  for 
round  rods  while  square  and  flat  rods  were  not  quite  so  strong. 
Corrugated  bars  gave  higher  results.  The  concrete  was  a 
1:2:4  mix.  Pull  out  tests  on  specimens  of  the  same  mix  usually 
gave  higher  results.  There  does  not  seem  to  be  any  relation 


PLAIN  CONCRETE  81 

between  the  size  of  rod  and  the  unit  bond  stress.  The  bond 
strength  of  a  1:3:6  concrete  is  about  20  or  30  per  cent  less  than 
that  of  a  1:2:4  mix. 

102.  Elastic  Limit  and  Modulus  of  Elasticity  of  Concrete. — As 
the  stress  strain  curve  for  concrete  is  not  a  straight  line  through- 
out any  part  of  its  length  and  as  the  concrete  is  subject  to  a 
permanent  deformation  even  for  a  small  load,  concrete  may  be 
said  to  have  no  true  elastic  limit.     There  appears  to  be  a  limit, 
however,  to  the  stress  that  can  be  repeated  indefinitely  without 
continuing  to  add  appreciably  to  the  deformation.     This  limit 
may  be  taken  as  the  elastic  limit,  or  yield  point,  for  all  practical 
purposes.     From  the  results  of  tests  it  appears  that  this  limit 
is   usually   somewhere    between  40   and   60   per   cent   of    the 
ultimate. 

As  the  stress  strain  curve  for  concrete  is  a  curved  line,  the 
modulus  of  elasticity  is  not  a  constant  through  any  appreciable 
range  of  stress.  One  way  to  determine  the  modulus  of  elasticity 
is  to  take  the  slope  of  the  curve  at  the  origin.  Another,  and 
perhaps  a  better,  way  is  to  compute  the  secant  modulus  for  a 
load  of  300  or  500  Ib.  per  square  inch,  or  for  a  load  equal  to  about 
J^  of  the  ultimate.  The  second  way  usually  gives  a  value 
considerably  less  than  that  obtained  by  the  first. 

For  a  concrete  one  month  old  and  for  a  stress  of  500  Ib.  per 
square  inch,  the  secant  modulus  of  elasticity  for  a  1:2:4  mix  will 
generally  be  between  2,000,000  and  2,500,000  Ib.  per  square  inch, 
and  between  1,500,000  and  2,000,000  Ib.  per  square  inch  for  a 
1:3:6  mix.  If  the  modulus  of  elasticity  is  computed  from  the 
slope  of  the  curve  at  the  origin,  the  value  obtained  will  probably 
be  from  20  to  50  per  cent  higher  than  the  secant  modulus  at  500 
Ib.  per  square  inch. 

In  general,  the  modulus  of  elasticity  increases  with  the  richness 
of  mix  and  the  age,  but  varies  greatly  with  different  aggregates. 

103.  Yield  of  Concrete. — Yield  may  be  defined  as  the  volume 
of  concrete  that  may  be  obtained  from  given  quantities  of  cement, 
fine  and  coarse  aggregates.     Other  things  being  equal,   those 
concrete  materials  should  be  used  which  will  give  the  greatest 
yield  of  concrete.     This  means  that  less  quantities  of  the  ma- 
terials will  be  required  for  a  given  volume  of  concrete  and,  conse- 
quently, the  cost  of  the  concrete  will  be  less,  assuming  that  the 
materials  are  purchased  by  volume  and  that  the  prices  are  the 
same  for  all  varieties  of  the  same  kind  of  materials. 

6 


82  MATERIALS  OF  CONSTRUCTION 

104.  Expansion  and  Contraction  of  Concrete. — Experiments 
have  shown  that  concrete  will  shrink  a  little  when  hardening  in 
air,  and  that  when  it  is  hardening  under  water  it  will  keep  about 
the  same  volume  or  perhaps  swell  a  trifle.     The  coefficient  of 
expansion  for  concrete  is  about  0.000006  per  degree  Fahrenheit. 
The  coefficient  of  expansion  increases   but  very  little   with  an 
increase  in  the  richness  of  the  mix.     The  fact  that  an  average 
crushed  stone  concrete  has  a  coefficient  of  expansion  practically 
equal  to  that  of  steel  is  of  importance  in  reinforced  concrete 
work. 

105.  Miscellaneous    Properties     of     Concrete. — Weight    per 
Cubic  Foot. — The  weight  per  cubic  foot  of  concrete  may  vary 
considerably,  due  to  the  kind  of  materials  used  for  aggregates. 
The  weight  also  varies  directly  with  the  richness  of  mix  and  the 
density.     A  concrete  made  from  sand  and  crushed  stone  usually 
weighs  from  135  to  160  Ib.  per  cubic  foot.     For  practical  purposes, 
the  weight  of  concrete  may  be  assumed  to  be  145  or  150  Ib.  per 
cubic  foot. 

Absorption. — The  absorption  of  water  by  concrete  may  be  quite 
small  or  very  large,  depending  upon  the  richness  and  density  of 
mix,  kind  of  materials  used  for  aggregates,  thoroughness  of 
mixing,  care  in  placing,  etc.  In  general,  the  same  factors  that 
tend  to  make  concrete  impervious  will  also  tend  to  make  it 
non-absorptive. 

Abrasion. — The  abrasive  resistance  of  a  concrete  depends 
primarily  upon  the  abrasive  resistance  of  the  mortar.  Of  course, 
if  the  surface  of  the  concrete  is  worn  away  so  that  the  coarse 
aggregate  is  exposed,  the  abrasive  resistance  of  the  coarse 
aggregate  will  have  some  influence  on  the  abrasive  resistance  of 
the  concrete.  The  abrasive  resistance  of  the  mortar  depends 
upon  the  ability  of  the  cement  to  hold  the  sand  grains  together 
and  also  upon  the  abrasive  resistance  of  the  sand  grains 
themselves. 

106.  Working  Stresses  and  Factor  of  Safety  for  Concrete.— 
The    following    working    stresses    are    recommended    by    the 
Committee  on  Concrete  and  Reinforced  Concrete  of  the  American 
Society  of  Civil  Engineers. 

The  allowable  compressive  stress  on  a  short  plain  concrete 
column  or  pier  (whose  length  does  not  exceed  12  diameters)  is 
22.5  per  cent  of  the  strength  at  28  days,  or  450  Ib.  per  square 
inch  for  2,000  Ib.  concrete.  The  factor  of  safety  is  4.5. 


PLAIN  CONCRETE  83 

The  extreme  fiber  stress  in  compression  in  a  reinforced  concrete 
beam,  calculated  on  the  assumption  of  a  constant  modulus  of 
elasticity  for  concrete  under  working  stresses,  may  be  allowed  to 
reach  32.5  per  cent  of  the  compressive  strength  at  28  days,  or 
650  Ib.  per  square  inch  for  2,000  Ib.  concrete.  The  apparent 
factor  of  safety  is  3.1  while  the  actual  factor  is  larger. 

Where  pure  shearing  stress  occurs,  uncombined  with  compres- 
sion normal  to  the  shearing  surface  and  with  all  tension  normal 
to  the  shearing  plane  provided  for  by  reinforcement,  a  shearing 
stress  of  6  per  cent  of  the  compressive  strength  at  28  days,  or 
120  Ib.  per  square  inch  for  2,000  Ib.  concrete,  may  be  allowed. 
The  factor  of  safety  in  this  case  is  between  6  and  7. 

When  the  shear  is  combined  with  an  equal  compression,  as  on  a 
section  of  a  column  at  45  degrees  with  the  axis,  the  stress  may 
equal  one-half  of  the  compressive  stress  allowed.  For  ratios  of 
compressive  stress  to  shear  between  0  and  1,  proportionate 
shearing  stresses  shall  be  used.  This  gives  a  factor  of  safety  of 
about  4.5. 

The  bonding  stress  between  concrete  and  plain  reinforcing 
bars  may  be  assumed  at  4  per  cent  of  the  compressive  strength 
at  28  days,  or  80  Ib.  per  square  inch  for  2,000  Ib.  concrete;  and 
in  the  case  of  drawn  wire,  2  per  cent,  or  40  Ib.  per  square  inch 
for  2,000  Ib.  concrete.  The  factors  of  safety  are  about  4.5  and 
2.25. 

It  is  recommended  that  the  modulus  of  elasticity  of  concrete  in 
compression  be  assumed  as  ^5  of  that  of  steel  (2,000,000  Ib.  per 
square  inch  for  a  good  1:2:4  concrete  1  month  old).  While  this 
assumption  is  not  accurate,  it  will  give  safe  results. 

107.  Rubble  Concrete. — This  is  a  concrete  in  which  stones 
of  a  large  size  are  handled  and  embedded  separately.  Rubble 
concrete  construction  is  suitable  only  for  massive  work  where 
the  concrete  is  not  less  than  3  or  4  ft.  thick.  The  saving  over 
the  cost  of  ordinary  concrete  is  very  little  except  in  instances 
where  the  large  stones  cari  be  very  cheaply  procured  and  handled. 
The  usual  procedure  is  to  drop  the  large  stones  in  the  concrete 
and  then  spade  the  concrete  around  the  stones  so  as  to  release  the 
air  and  make  a  good  bond.  The  large  stones  should  be  clean  and 
the  joints  between  the  stones  should  be  at  least  4  in.  thick  and 
well  filled  with  wet  concrete.  The  concrete  should  be  wet 
enough  to  flow  readily  around  the  stones. 


84  MATERIALS  OF  CONSTRUCTION 

G.  CONCRETE  STONE,  BLOCK,  AND  BRICK 

108.  Definitions  and  Classifications. — Concrete  stone  may  be 
defined  as  any  precast  concrete  units  of  ordinary  size  which  are 
used  for  construction  purposes. 

Concrete  blocks  are  concrete  stones  which  are  considerably 
larger  than  ordinary  brick.  The  blocks  are  of  several  shapes, 
varieties,  and  sizes.  Most  concrete  blocks  (except  those  used  for 
purposes  of  ornamentation)  are  hollow  so  as  to  form  air  spaces  in 
the  walls  and  save  weight  and  materials.  There  is  no  standard 


FIG.  21. — Cross  sections  of  some  concrete  blocks. 

size,  though  the  length  is  usually  16  or  24  in.,  the  height  8  or  9  in., 
and  the  thickness  8,  10,  or  12  in. 

Concrete  brick  usually  are  of  the  same  size  as  ordinary  building 
brick  and  are  usually  made  solid,  though  some  makes  have 
grooves  or  hollows  in  the  top  and  bottom. 

Concrete  stone  may  be  divided  into  two  classes  according  to 
use:  (1)  units  for  structural  use  primarily,  such  as  ordinary  solid 
or  hollow  blocks  and  brick ;  and  (2)  units  designed  primarily  for 
purposes  of  architectural  effect  and  ornamentation,  such  as  the 
specially  molded  shapes  or  specially  faced  blocks  or  brick. 

Concrete  stone  may  also  be  classified  according  to  the  method 
of  manufacture.  The  three  general  methods  in  use  are  the  dry 
tamp,  pressure,  and  wet-cast  methods.  Concrete  stone  for  orna- 
mental purposes  is  usually  made  in  special  molds  by  the  dry  tamp 
method. 

109.  Materials  for  Concrete  Stone. — The  materials  should  be 
chosen  according  to  the  principles  governing  the  selection  of 
materials  for  good  concrete,  except  that  the  coarse  aggregate 
should  be  a  well-graded  crushed  stone  or  gravel  that  will  pass 
a  %-in.  sieve  and  be  retained  on  a  M-in.  sieve. 

110.  Proportions. — The  proportions  for  concrete  blocks  should 
be  1  part  of  good  portland  cement  to  not  over  2}^  or  3  parts  of 
good   sand  and  to  not  over  3  or  4  parts  of  coarse  aggregate. 
That  is,  the  leanest  allowable  mix  is  a  1:3:4.     When  the  coarse 


PLAIN  CONCRETE  85 

aggregate  is  omitted,  the  proportions  should  be  1  part  of  cement 
to  not  over  4  parts  of  good  sand. 

The  limiting  proportions  for  cement  brick,  which  usually 
contain  no  coarse  aggregate,  are  the  same  as  those  for  concrete 
blocks. 

In  general,  the  proportions  should  be  such  that  the  concrete 
stone  will  pass  the  specifications  given  in  a  following  article. 

111.  Consistency. — The  best  consistency  is  one   where  the 
mixture  will  just  retain  its  shape  when  the  molds  are  removed 
immediately  after  the  concrete  has  been  deposited  and  pressed 
in  place.     This  consistency  is  much  wetter  than  that  usually  used 
in  the  dry  tamp  method  and  a  little  wetter  than  that  used  in 
the   pressure  process.     The   consistency  used  in  the   wet-cast 
method  is  frequently  too  wet  to  secure  the  best  results.     A  con- 
sistency that  is  too  dry  makes  the  concrete  porous  and  increases 
its  absorptive  powers  besides  tending  to  reduce  the  strength. 

112.  Mixing  and  Molding. — The  mixing  may  be  done  either 
by  hand  or  machine.     (See  articles  on  hand  and  machine  mixing 
for  discussions  of  these  methods.) 

The  molding  may  be  done  either  by  hand  or  machine  except 
in  the  pressure  process  where  a  machine  is  required.  Concrete 
blocks  and  brick  for  structural  purposes  are  usually  molded  by 
machines  while  especially  molded  blocks  are  usually  molded  by 
hand.  At  present  there  are  many  different  kinds  of  molding 
machines  used  in  the  manufacture  of  concrete  stone.  The 
construction  of  the  machines  varies  with  the  consistency  of  the 
mix  and  the  methods  used  for  compacting  the  concrete. 

The  following  are  the  three  methods  most  frequently  used  in 
the  manufacture  of  concrete  blocks  and  brick: 

(a)  Dry  Tamp  Process. — The  materials  are  first  mixed  to  a 
damp  consistency  and  are  then  thoroughly  tamped  in  the  molds 
by  hand  or  machine  tampers.     Usually  too  little  water  is  used 
in  this  process.     This  method  is  nearly  always  used  in  making 
concrete  stone  of  special  shape  or  surface  finish  as  the  molds  may 
be  made  of  any  desired  shape  and  size.     The  tamping  is  usually 
done  by  hand. 

(b)  Pressure  Process. — A  somewhat  wetter  mixture  is  used 
than  in  the  dry  tamp  process.     The  concrete  is  then  placed  in 
the  molds  and  pressure  is  applied  either  by  mechanical  levers 
or  by  a  hydraulic  piston. 

(c)  Wet-cast  Process. — In  this  process  the  consistency  is  such 


86  MATERIALS  OF  CONSTRUCTION 

that  the  concrete  will  readily  flow.  The  mixture  is  poured 
into  the  molds  and  then  thoroughly  puddled  to  release  any 
entrained  air  and  to  get  the  large  particles  away  from  the  sur- 
faces. No  tamping  or  mechanical  pressure  is  used.  Frequently 
too  much  water  is  used. 

In  the  first  two  methods  the  concrete  is  dry  enough  so  that 
the  molds  can  be  removed  immediately  from  the  blocks,  while 
in  the  last  method  the  molds  cannot  be  removed  until  after  the 
concrete  has  set.  If  either  of  the  first  two  methods  is  used, 
care  should  be  taken  to  secure  density  and  uniformity  of  com- 
pactness in  the  blocks. 

113.  Surface  Finishes. — A  variety  of  pleasing  surface  finishes 
may  be  secured  with  concrete  blocks  and  brick.     For  a  descrip- 
tion of  a  number  of  ways  of  finishing  the  surface,  see  article  on 
" Surface  Finish." 

Another  way  is  to  have  one  of  the  faces  of  the  mold  so  shaped 
that  the  exposed  face  of  the  block,  when  placed  in  a  wall,  will 
have  some  pleasing  shape  such  as  some  surface  finish  of  stone 
masonry,  etc.  Special  molds  can  be  made  to  give  a  great  variety 
of  designs  of  cornices,  rails,  window  seats,  ornaments,  etc. 

Still  another  way  is  to  place  a  facing  layer  of  a  selected  fine 
material  next  to  the  face  mold,  this  layer  becoming  intimately 
bonded  with  the  body  of  the  block  in  the  process  of  molding. 

Variety  of  color  may  be  secured  by  using  different  colored 
stones  or  sands  in  the  facing  layer  or  by  adding  coloring  matter 
when  the  materials  are  mixed.  Only  the  purest  mineral  colors 
should  be  used,  as  coloring  matter  (especially  when  impure) 
tends  to  destroy  the  binding  qualities  of  the  cement.  Sometimes 
the  coloring  may  be  secured  by  applying  a  cement  stain  to  the 
desired  surfaces. 

114.  Curing  and  Aging. — In  curing,  care  should  be  taken  to 
prevent  the  drying  out  of  the  blocks  during  their  first  hardening. 
After  the  molds  are  removed,  the  blocks  should  be  protected 
from  wind  currents,  sunlight,  dry  heat,  and  freezing  for  at  least 
a  week.     During  this  time  additional  moisture  should  be  supplied 
to  the  blocks  by  sprinkling,  or  some  other  method  equally  as 
good,  at  least  once  a  day.     After  the  first  week  the  blocks  should 
be  sprinkled,  or  otherwise  moistened,  at  occasional     intervals 
until   they   are   used.     When   cured   by   any   natural   process, 
concrete  blocks  should  not  be  used  for  construction  purposes 
until  they  are  at  least  three  weeks  old. 


PLAIN  CONCRETE  87 

The  curing  of  concrete  stone  products  may  be  accelerated  by 
placing  them  (as  soon  as  possible  after  they  are  removed  from 
the  molds)  in  an  atmosphere  of  moist  steam  for  at  least  48  hours. 
The  temperature  of  the  curing  room  should  be  between  100  and 
130  degrees  Fahrenheit.  The  saturated  steam  provides  heat 
and  moisture  and  accelerates  the  hardening  or  setting  of  the 
concrete  without  causing  the  concrete  to  lose  any  of  its  moisture. 
After  removal  from  the  steam  curing  room,  the  concrete  blocks 
should  be  stored  for  at  least  8  days  before  using. 

115.  Properties  of  Concrete  Blocks  and  Brick. — Concrete 
blocks  and  brick  are  usually  not  so  strong  as  plain  concretes  of 
the  same  proportions.  This  is  probably  due  to  the  fact  that  the 
consistencies  used  are  not  the  ones  which  will  give  the  greatest 
strength.  Blocks  made  by  the  dry  tamp  and  pressure  processes 
often  contain  too  little  water  while  those  made  by  the  wet-cast 
process  usually  contain  too  much  water. 

Good  concrete  blocks  and  brick  should  pass  the  following  tests : 

(a)  Transverse  Test. — When  subjected  to  transverse  tests  at 
an  age  of  28  days,  the  modulus  of  rupture  should  average  more 
than  150  Ib.  per  square  inch  and  should  not  be  less  than  100  Ib. 
per  square  inch  in  any  individual  case. 

(b)  Compression  Test. — The  ultimate  compressive  strength  of 
solid  blocks  at  the  age  of  28  days  should  average  more  than  1 ,500 
Ib.  per  square  inch  and  should  not  be  less  than  1,000  Ib.  per 
square  inch  in  any  individual  case. 

The  ultimate  compressive  strength  of  hollow  blocks  at  the 
age  of  28  days  should  average  more  than  1,000  Ib.  per  square 
inch,  and  should  not  be  less  than  700  Ib.  per  square  inch  in  any 
individual  case.  In  calculating  the  results,  no  reductions  shall 
be  made  for  the  hollow  spaces  in  the  blocks. 

The  allowable  working  stress  in  compression  should  not  exceed 
167  Ib.  per  square  inch  of  gross  area  for  hollow  blocks,  and  300 
Ib.  per  square  inch  of  gross  area  for  solid  blocks. 

(c)  Absorption  Test. — The  samples  shall  be  dried  to  constant 
weight  at  a  temperature  not  exceeding  212  degrees  Fahrenheit. 
After  drying,  the  samples  shall  be  immersed  in  clean  water  for 
48    hours.     The    percentage    of    absorption    (weight    of    water 
absorbed  divided  by  the  dry  weight  of  the  sample)  should  not 
average  over  12  per  cent  and  should  not  exceed  18  per  cent  in 
any  individual  case. 

Full-sized  blocks  or  brick  shall  be  tested  whenever  possible. 


88  MATERIALS  OF  CONSTRUCTION 

The  number  of  samples  for  any  one  test  should  not  be  less  than 
three. 

116.  Uses  of  Concrete  Blocks  and  Brick. — Blocks  made  of 
molded  concrete  can  be  used  to  advantage,  as  a  substitute  for 
solid  concrete,  brick,  or  stone,  in  the  construction  of  walls  that 
are  thin  or  which  carry  only  light  loads,  such  as  building  walls, 
partitions,  etc.  Solid  concrete  is  not  satisfactory  for  such  pur- 
poses on  account  of  the  expense  of  forms,  the  difficulty  of  securing 
a  proper  finish,  and  the  prevention  of  the  formation  of  cracks 
Concrete  blocks  are  usually  made  of  such  shapes  and  sizes  that 
they  will  form  a  wall  containing  hollow  spaces,  thus  increasing 
the  stability  of  the  wall  and  forming  dead  air  spaces  as  well  as 
decreasing  the  weight. 

Concrete  brick  are  usecl  as  a  substitute  for  ordinary  building 
brick. 

Especially  molded  and  finished  concrete  blocks  and  brick 
are  used  for  various  purposes  of  architectural  detail  and 
ornamentation. 


CHAPTER  VI 

BUILDING  STONE 

A.  CLASSIFICATIONS  AND  DESCRIPTIONS 

117.  Building  Stone  in  General. — Building  stones  include  all 
of  those  stones  or  rocks  that  are  used  in  masonry  construction. 
The  qualities  which  are  the  most  important  in  stone  used  for 
construction  purposes  are  cheapness,  durability,  strength,  and 
beauty.     In  general,  the  hardest,  densest,  toughest,  and  most 
uniform  stone  will  be  the  best  stone  to  use. 

The  fitness  of  a  stone  for  structural  purposes  may  be  approxi- 
mately determined  by  the  examination  of  a  fresh  fracture.  This 
fracture  should  be  bright,  clean,  sharp,  without  any  loose  grains 
and  be  free  from  a  dull  earthy  appearance.  An  even  fracture, 
when  the  surfaces  of  division  are  planes  in  definite  positions,  is 
characteristic  of  a  crystalline  structure.  An  uneven  fracture, 
when  the  broken  surface  presents  sharp  projections,  is  character- 
istic of  a  granular  structure.  A  slaty  fracture  gives  an  even 
surface  for  planes  of  division  parallel  to  the  laminations,  and 
uneven  surfaces  for  other  directions  of  division.  A  conchoidal 
fracture  presents  smooth  concave  and  convex  surfaces,  and  is 
characteristic  of  a  hard  and  compact  structure.  An  earthy 
fracture  leaves  a  rough,  dull  surface  and  indicates  softness  and 
brittleness. 

The  stone  should  contain  no  material,  either  in  the  form  of 
seams  or  veins,  that  is  not  thoroughly  cemented  together. 
Stone  containing  much  mica,  pyrites,  or  glass  seams  usually  are 
not  very  durable. 

Only  about  half  of  all  of  the  stone  quarried  is  used  for  structural 
purposes,  the  other  part  being  used  for  roads  and  pavements, 
crushed  stone  for  railroad  ballast  and  concrete,  etc. 

118.  Classifications  of  Building  Stone. — Building  stone  may 
be  classified  according  to  geological  position,  physical  structure, 
or   chemical    composition.     The  geological  position  of  a  rock 
has  but  very  little  influence  upon  its  properties  as  a  building 
stone. 

89 


90  MATERIALS  OF  CONSTRUCTION 

A.  Geological  Classification 

1.  Igneous  rocks  which  are  formed  by  a  consolidation  of  the  material 
from  a  fused  or  partly  fused  condition,  such  as  greenstone,  basalt,  lava,  etc. 

2.  Sedimentary  rocks  which  are  formed  by  a  consolidation  of  material 
transported  and  deposited  by  water,  such  as  sandstones,  limestones,  and 
clays. 

3.  Metamorphic  rocks  which  are  formed  by  a  gradual  change  in  the 
structure  and  character  of  igneous  or  sedimentary  rocks  due  to  their  expo- 
sure to  heat,  water,  pressure,  etc.     Some  examples  are  the  marbles  and  slates. 

B.  Physical  Classification 

1.  Stratified  rocks  which  are  formed  in  layers,  such  as  the  sandstones, 
marbles,  limestones,  and  some  of  the  clays  and  slates.     Their  structure  is 
either  crystalline  or  granular  or  a  combination  of  both. 

2.  Unstratified  rocks  which  are  not  formed  in  layers.     These  rocks  are 
usually  made  of  crystalline  grains  strongly  adhering  together.     Some  ex- 
amples are  the  granites,  traps,  basalts,  etc. 

C.  Chemical  Classification 

1.  Siliceous  rocks  in  which  silica  is  the  most  important  chemical  element, 
such  as  the  granites,  syenites,  mica-slate,  basalt,  trap,  quartz,  sandstone, 
etc. 

2.  Argillaceous  rocks  (clayey  rocks)  in  which  the  alumina  governs  the 
characteristic  properties,  such  as  the  clays  and  slates.     These  stones  are 
usually  not  very  durable. 

3.  Calcareous  rocks  in  which  carbonate  of  lime  is  the  important  element, 
such  as  the  marbles  and  limestones.     The  more  compact  of  these  stones  are 
the  more  durable  ones. 

119.  Granite,  Gneiss,  and  Trap. — Granite  is  used  more  for 
structural  purposes  than  any  other  igneous  rock,  and  is  the 
strongest  and  most  durable  of  all  the  stones  in  common  use. 
It  is  very  hard  and  tough  and,  consequently,  is  difficult  to  cut 
and  shape.  However,  it  may  be  quarried  in  simple  pieces  with- 
out much  difficulty  as  it  breaks  easily  along  its  planes  of  weakness, 
which  are  at  right  angles  to  each  other.  Granite  is  used  for 
foundations,  base  courses,  walls,  columns,  steps,  paving  blocks, 
etc. 

Gneiss  has  the  same  composition  and  about  the  same  appear- 
ance as  granite  and  is  found  in  the  same  localities.  It  differs 
from  granite  by  being  usually  arranged  in  more  or  less  parallel 
layers,  which  makes  the  work  of  quarrying  less  difficult  and 
expensive.  This  stone  is  used  for  foundation  walls,  courses, 
street  paving,  curbs,  etc. 


BUILDING  STONE  91 

Trap  is  the  strongest  and  one  of  the  most  durable  of  all  building 
stones.  It  is  also  very  tough  and  usually  has  no  planes  of  cleav- 
age. As  it  is  difficult  to  quarry  and  work,  trap  is  used  very  little 
for  structural  purposes. 

120.  Limestone,  Marble,   Sandstone,  and  Slate. — Limestone 
is  a  stone  which  contains  calcium  carbonate  as  its  main  constitu- 
ent.    It  is  very  widely  distributed  and  much  used  in  building 
construction,  probably  ranking  next  to  granite  in  this  respect. 
Limestone  differs  greatly  in  color,  composition,  and  structural 
qualities,  because  of  the  character  of  the  deposits  and  their 
chemical  composition. 

Marble  is  a  limestone  which  has  been  subjected  to  a  metamor- 
phic  action  and  has  had  its  structure  changed  to  a  more  crystal- 
line form.  Its  original  color  is  usually  changed  and  sometimes 
lost  during  this  metamorphic  action.  Marble  has  a  variety  of 
colors,  is  very  beautiful,  and  is  much  used  for  interior  decorations. 
Often  the  name  " marble"  is  improperly  used  by  applying  it  to 
any  limestone  that  will  take  a  polish. 

Sandstone  is  composed  of  grains  of  quartz  sand  which  are 
cemented  together  by  means  of  silica,  iron  oxide,  calcium  car- 
bonate, or  clayey  materials  to  form  a  solid  rock.  This  stone 
differs  greatly  in  color,  hardness,  and  durability,  but  some  are 
very  suitable  for  use  in  outside  construction.  The  durability 
of  the  sandstone  depends  both  upon  its  physical  and  its  chemical 
composition.  The  best  has  silica  as  a  cementing  material  and 
is  usually  soft  wheji  quarried  but  becomes  harder  upon  exposure. 
Sandstone  having  iron  oxide  as  a  cementing  material  ranks  next 
in  durability,  followed  by  that  having  calcium  carbonate,  while 
the  one  having  clayey  matter  is  the  poorest.  Sandstone  is  easier 
to  quarry  and  work  than  limestone.  Sandstone  is  used  a  great 
deal  in  building  construction. 

Slate  is  ordinarily  composed  of  a  siliceous  clay  which  has  been 
deposited  in  thin  layers  on  a  sea  bed  and  later  metamorphosed 
and  compacted  by  pressure  into  a  solid  rock.  Slate  can  be  split 
into  thin  sheets  and  is  tough,  strong,  and  non-absorptive.  It  is 
used  for  roofing  and  some  interior  work  in  buildings. 

B.  STONE  QUARRYING  AND  CUTTING 

121.  Hand  Methods  of  Stone  Quarrying. — No  matter  what 
method  of  quarrying  is  used,  it  is  first  necessary  to  remove  the 
surface  soil  from  the  rock.     The  stone  may  be  quarried  by 


92 


MATERIALS  OF  CONSTRUCTION 


means  of  hand  tools,  machine  tools,   explosives,   or  by  some 
combination  of  these  methods. 

Hand  methods  may  be  used  when  the  stone  occurs  in  thin  beds. 
The  principal  tools  used  are  the  pick,  crowbar,  drill,  hammer, 
wedge,  and  plug  and  feathers.  In  quarrying,  rows  of  holes,  which 
are  from  %  to  %  in.  in  diameter  and  a  few  inches  apart, are 
drilled  in  the  rock  by  means  of  the  drill  and  hammer.  The 


~*   « 


FIG.  22. — Cross  section  of  "Jackhammer  Sinker"  drill.     (I nger soil-Rand  Co.) 

distance  between  rows  usually  depends  upon  the  dimensions  of 
the  desired  stone.  In  drilling,  a  man  holds  the  drill  in  one  hand 
and  drives  it  with  a  hammer  in  the  other  hand,  rotating  the  drill 
a  little  between  blows.  Sometimes  one  man  holds  the  drill  and 
another  man  drives  it  with  a  heavy  hammer  or  sledge.  This  kind 
of  drill  is  called  a  jumper.  Another  kind  of  hand  drill  is  the  churn 
drill  which  is  a  heavy  drill  about  6  or  8  ft.  long.  This  drill  is 
raised  by  the  workman  who  lets  it  fall  in  the  desired  place,  then 
catches  it  on  the  rebound,  rotates  it  a  little  while  raising  it,  and 
lets  it  fall  again,  thus  cutting  a  hole  in  the  rock  without  the  aid  of 
a  hammer.  For  deep  holes,  a  churn  drill  is  more  economical  than 
a  jumper  drill. 


BUILDING  STONE  93 

After  the  holes  are  drilled,  a  plug,  inserted  between  two 
feathers,  is  placed  in  each  hole.  The  plug  is  a  narrow  steel  wedge 
with  plane  faces,  and  the  feathers  are  wedges  which  are  flat  on 
one  side  and  rounded  on  the  other.  Then  the  plugs  in  all  of  the 
holes  are  pounded  in  at  the  same  time  until  they  exert  a  force 
that  is  large  enough  to  split  the  rock  along  the  line  of  holes. 

122.  Machine    Methods    of    Quarrying. — Machine    methods 
include  the  use  of  machines  driven  by  steam,  compressed  air,  or 
electric  motors  to  drill  the  holes  or  cut  narrow  channels  in  the 
rock.     The  machine  drills  are  divided  into  two  classes — percus- 
sion drills  and  rotary  drills.     In  a  percussion  drill,  the  cutting 
tool  resembles  a  hand  drill.     This  drill  is  operated  by  a  cylinder 
using  steam  or  compressed  air,  or  by  an  electric  motor.     An 
automatic  device  rotates  the  drill  a  little  between  strokes.     In  a 
rotary  drill,  the  cutting  tool  is  a  hollow  tube  with  a  cutting  edge 
made  of  sharp  teeth  or  diamonds.     This  cutting  edge  is  kept  in 
contact  with  the  rock  while  the  drill  is  revolved,  thus  cutting  a 
hole  through  the  rock. 

When  large  rectangular  blocks  of  stones  are  desired,  a  special 
machine  called  a  "channeler"  is  often  used.  This  machine 
operates  on  a  track  or  guide  bars  and  carries  a  number  of  cutters 
which  cut  deep  narrow  channels  in  the  rock  as  the  machine 
slowly  moves  along. 

After  the  holes  are  drilled,  the  rock  is  broken  off  by  means  of 
plugs  and  feathers  or  by  means  of  explosives  inserted  in  the  holes. 

Stone  is  rarely  ever  quarried  by  one  method  alone.  The  use  of 
a  combination  of  two  methods  is  very  common  and  that  of  three 
methods  is  not  infrequent. 

123.  Explosives  Used  in  Quarrying. — Explosives  may  be  used 
instead  of  plugs  and  feathers  to  split  off  the  stone  after  the  drill 
holes  have  been  made.     The  explosive  is  placed  in  the  holes  in 
the  proper  amounts,  and  the  pressure  (tamping)  is  provided  by  a 
little  moist  sand,  clay,  packed  paper,  etc.  tamped  on  top.     In 
the  case  of  nitro-glycerine,  a  little  water  on  the  explosive  provides 
all  of  the  tamping  necessary. 

The  explosives  used  in  quarrying  are  usually  gunpowder  or 
dynamite  and  sometimes  nitro-glycerine.  The  gunpowder  must 
be  a  coarse,  slow  acting  kind  (commonly  known  as  "  blasting 
powder").  It  is  exploded  by  means  of  a  fuse  or  electric  spark. 

Dynamite  consists  of  some  granular  substance  (such  as  saw- 
dust) saturated  with  nitro-glycerine.  True  dynamite  contains  at 


94 


MATERIALS  OF  CONSTRUCTION 


least  50  per  cent  of  nitroglycerine,  while  the  granular  absorbent 
is  an  inert  material.  False  dynamite  may  contain  as  little  as 
15  per  cent  of  nitro-glycerine,  but  the  absorbent  material  contains 
at  least  one  other  explosive.  The  other  explosive  is  usually 
oxygen  which  is  liberated  in  large  quantities  by  the  explosion 
and  aids  in  effecting  the  complete  combustion  of  the  gases  of  the 
nitro-glycerine . 

Nitro-glycerine  is  a  fluid  made  by  mixing  glycerine  with  nitric 
or  sulphuric  acid.  It  is  rarely  used  in  quarrying  as  it  acts  too 
quickly  and  tends  to  shatter  the  rock  very  much. 


UK    23 

0 

3 

DOUBLE  FACE  MAMMS.R                                         | 

— 

FACE  HAMMER 

'  

n 

MO) 

SI 

\  / 

"1          ~T^::> 

V 

FIGS.  23-40. — Tools  used  in  stone  cutting. 

Dynamite  and  nitro-glycerine  are  exploded  by  means  of  a 
percussion  cap  which  is  ignited  by  a  fuse  or  an  electric  spark. 
A  percussion  cap  is  a  hollow  cylinder  made  of  copper  and  has  one 
end  closed.  This  cylinder  is  about  y±  in.  in  diameter  and  1  or 
2  in.  long.  It  contains  a  cement  made  of  fulminate  of  mercury 
and  some  inert  material. 

124.  Stone  Cutting. — In  stone  cutting,  various  tools  are  used, 
such  as  stone  hammers,  picks,  axes,  points,  chisels,  mallets, 
pneumatic  hammers,  etc.  These  tools  are  often  different  in 


BUILDING  STONE 


95 


shape  from  ordinary  tools  of  the  same  name.  An  examination  of 
the  sketches  of  these  tools  will  furnish  all  of  the  description 
necessary,  while  their  uses  will  be  indicated  in  the  following 
paragraphs. 

Building  stone  are  divided  into  three  general  classes  and 
various  subdivisions  according  to  the  finish  of  the  surfaces 
(from  Trans.  Am.  Soc.  Civ.  Eng.,  Vol.  6). 


FIG.  41. — Quarry-faced          FIG.  42. — Pitched-faced  FIG.  43. — Drafted 

squared  stone.  squared  stone.  stone. 


FIG.  44. — Rough-pointed  FIG.  45. — Fine- 

face  finish.  pointed  face  finish. 


FIG.  46.— Crandalled 
face  finish. 


1 

^ 

.-.:.    :  .    I 

FIG.  47. — Axed  or  pean- 
hammered  face  finish. 


FIG.  48.— Bush- 
hammered  face  finish. 


FIG.  49. — Raised 
diamond  panel. 


1.  Rough  or  Unsquared  Stone 

This  class  includes  all  stone  that  are  used  as  they  come  from 
the  quarry  without  any  special  preparation. 

2.  Stone  Roughly  Squared  antf  Dressed 

This  class  includes  stone  that  are  roughly  dressed  on  beds  and 
joints  with  the  face  hammer  or  axe.  The  distinction  between 
this  class  and  the  third  class  lies  in  the  closeness  of  the  joints. 
When  the  dressing  on  the  joints  is  such  that  the  general  thickness 
of  mortar  required  is  one-half  inch  or  more,  the  stone  properly 
belong  to  this  class.  There  are  three  subdivisions: 

(a)  Quarry  faced  stone  are  those  whose  faces  are  left  untouched  as  they 
come  from  the  quarry. 

(6)  Pitched-faced  stone  are  those  in  which  the  edges  of  the  faces  are  made 
approximately  true  by  the  use  of  a  pitching  chisel. 

(c)  Drafted  stone  are  those  whose  faces  are  surrounded  by  a  chisel  draft, 
the  space  inside  being  left  rough.  This  method  is  not  ordinarily  used  on 
stone  of  this  (the  second)  class. 


96  MATERIALS  OF  CONSTRUCTION 

3.  Cut  Stone  or  Stone  Accurately  Squared  and  Finely  Dressed 

This  class  includes  all  stone  dressed  to  smooth  beds  and 
joints  so  that  the  thickness  of  the  mortar  joints  is  less  than  one- 
half  inch.  As  a  rule,  all  of  the  edges  of  cut  stone  are  drafted, 
and  between  the  drafts  the  stone  is  smoothly  dressed  by  one  of 
the  following  methods.  In  massive  construction  work,  the 
face  of  the  stone  is  often  left  rough. 

(a)  Rough-Pointed. — The  excess  of  material  is  removed  by  the  pick  or 
heavy  point  until  the  projections  vary  from  %  to  1  in.  This  method  is 
much  used  on  limestone  and  granite. 

(6)  Fine-Pointed. — The  projections  are  less  than  J^  in.  and  the  tool  used 
is  a  fine  point. 

(c)  Crandalled. — The  same  effect  is  produced  as  in  fine  pointed  stone, 
except  that  the  tool  marks  are  more  regular  and  with  J^-in.  projections. 
A  stone  is  said  to  be  cross  crandalled  when  it  is  crandalled  in  both  directions. 
The  tool  used  is  a  craridall. 

(d)  Axed  or  Paen  Hammered. — The  face  of  the  stone  is  covered  with 
parallel  chisel  marks. 

(e)  Tooth  Axed. — The  same  finish  as  fine-pointed  stone,  except  that  the 
tool  used  is  a  tooth  axe. 

(/)  Bush- Hammered. — Where  the  roughnesses  of  the  surface  are  pounded 
off  with  a  bush  hammer.  This  follows  the  rough  pointing  or  tooth  axing 
and  is  usually  used  only  on  limestone. 

(g}  Rubbed. — Where  the  sawn  surfaces  of  the  stone  are  smoothed  by  grit 
or  sandstone.  The  method  is  used  on  marbles  and  sandstones. 

(h)  Diamond  Panels. — Where  the  face  inside  the  draft  is  cut  to  flat  pyra- 
midal forms. 

C.  PROPERTIES  OF  BUILDING  STONE 

125.  Durability. — The  durability  of  a  stone  depends  upon  its 
ability  to  resist  the  destructive  actions  due  to  the  weather 
agencies.  The  determining  factors  of  durability  are  the  struc- 
ture, texture,  and  mineral  composition  of  the  stone.  Imperfec- 
tions, such  as  cracks,  joint  planes,  etc.,  allow  water  to  enter  and 
disintegration  to  start  through  the  action  of  frost.  A  coarse- 
grained or  porous  stone  usually  disintegrates  more  rapidly  than 
does  a  fine-grained  stone.  Different  mineral  compounds  in  the 
stone  also  influence  the  durability.  A  stone  containing  silica  or 
silicates  is  the  most  resistant  to  decay;  followed  by  that  contain- 
ing aluminates;  calcium  and  magnesium  carbonates;  iron  com- 
pounds; and  sulphides. 

An  increase  in  the  durability  of  the  stone  may  be  secured  by 
proper  seasoning  and  surface  finishing.  When  the  stone  is 


BUILDING  STONE  97 

green,  it  contains  much  quarry  sap  and  disintegrates  much  faster 
than  after  it  is  seasoned  and  the  quarry  sap  has  evaporated.  In 
dressing  the  stone,  care  should  be  taken  not  to  break  up  the 
grains  too  much  and  produce  very  small  fissures  through  which 
the  water  may  enter.  A  stone  resists  the  effects  of  both  pressure 
and  weathering  much  better  if  it  is  placed  on  its  natural  bed. 

The  best  way  to  determine  the  durability  of  the  stone  is  to 
examine  the  surfaces  of  stone  structures  which  have  been  exposed 
to  atmospheric  influences  for  years.  There  have  been  many 
artificial  tests  proposed,  such  as  specific  gravity,  hardness 
or  toughness,  compression,  cross-bending,  shear,  absorption, 
chemical,  freezing,  acid  and  microscopical  tests,  for  determining 
the  durability  of  the  stone,  but  none  of  these  tests  give  wholly 
satisfactory  results. 

The  following  table  gives  the  estimated  life  of  some  of  the 
building  stones.  The  values  are  approximate,  depending  upon 
the  variety  of  stone  and  place  where  it  is  used. 

APPROXIMATE  LIFE  OF  BUILDING  STONE 

Sandstone  may  last  from  20  to  200  years  according  to  kind  and  place. 
Limestone  may  last  from  20  to  40  years  according  to  kind  and  place. 
Marble  may  last  from  40  to  100  years  according  to  kind  and  place. 
Granite  may  last -from  75  to  200  years  according  to  kind  and  place. 
Gneiss  may  last  from  50  to  200  years  according  to  kind  and  place. 

126.  Action  of  Frost,  Wind,  Rain,  and  Smoke. — Frost  action,  or 
freezing,  disintegrates  a  stone  only  when  the  pores  are  practically 
filled  with  water  before  the  freezing  takes  place.  As  a  stone  is 
not  often  used  in  such  a  way  that  the  maximum  amount  of 
water  is  absorbed,  it  is  very  rare  that  a  good  building  stone  is 
injured  by  frost.  Only  a  stone  having  a  high  absorptive  power 
and  a  low  structural  strength  is  liable  to  be  damaged  by  freezing. 

A  gentle  wind  has  no  effect  on  the  stone  but  a  heavy  wind 
blows  rain,  dust,  sand  particles,  etc.  against  the  face  of  the  rock. 
The  sand  and  dust  particles  tend  to  wear  away  the  surface  by 
abrasion. 

Rain,  falling  on  the  stone,  penetrates  the  pores  and  tends  to 
dissolve  some  of  the  chemicals  in  the  stone.  Rain  water  may 
contain  some  acids  which  are  injurious  to  the  stone.  Also, 
there  is  the  effect  of  pattering  raindrops  and  flowing  water  wear- 
ing away  the  surface. 

Smoke,  which  usually  contains  sulphuric  or  carbonic  acid,  has 

7 


98  MATERIALS  OF  CONSTRUCTION 

a  bad  effect  on  the  stone,  as  these  acids,  as  well  as  the  nitric  acid 
in  the  air,  tend  to  cause  disintegration. 

127.  Action  of  Fire. — Fires,  such  as  destroy  ordinary  buildings, 
produce  temperatures  that  are  high  enough  to  injure  seriously 
the  exposed  building  stone.     The  injury  due  to  the  combined 
action  of  both  fire  and  water  is  usually  much  greater  than  that 
due  to  fire  alone.     Rapid  cooling,  by  the  application  of  water, 
of  the  exteriors  of  a  highly  heated  stone  tends  to  cause  it  to 
disintegrate. 

Any  stone  expands  upon  being  heated,  but  it  only  partly 
returns  to  its  original  dimensions  on  being  cooled.  This  increase 
or  set  is  very  small,  being  about  JK  oo  of  1  per  cent  of  the  length 
of  the  stone. 

Granite  usually  cracks  and  spalls  badly  when  exposed  to  fire. 
This  stone  has  a  low  fire  resistance. 

Gneiss  does  not  resist  fire  so  well  as  granite  does. 

Limestone  offers  a  high  resistance  to  fire  until  a  temperature 
of  about  1,100  degrees  Fahrenheit  is  reached  and  then  the  stone 
starts  to  decompose  and  crumble,  due  to  the  driving  off  of  the 
carbon  dioxide  and  the  flaking  of  the  quicklime  formed.  Lime- 
stone is  injured  more  by  slow  cooling  than  by  sudden  cooling. 

Marble  cracks  and  spalls  to  some  extent  at  temperatures  below 
that  at  which  calcination  begins.  After  that  temperature  is 
reached,  its  action  is  like  that  of  limestone. 

Sandstone,  especially  if  it  is  dense  and  non-porous,  offers  a 
better  resistance  to  fire  than  other  building  stone.  It  cracks 
less  than  any  other  stone,  and,  if  properly  placed,  these  cracks 
will  probably  be  horizontal.  Sandstone  having  silica  or  lime 
carbonate  for  a  cementing  material  resists  fire  better  than  a 
stone  bound  with  iron  oxide  or  clay. 

128.  Mechanical  Properties  of  Building  Stone. — The  following 
tables  give  some  average  values  of  the  strength  and  other  mechan- 
ical properties  of  the  principal  building  stone.     It  is  to  be  noted 
that  there  are  several  varieties  of  each  kind  of  stone  and  that  the 
results  obtained  by  testing  any  one  variety  may  vary  considerably 
from  the  average  given  in  the  table.     However,  most  any  variety 
of  stone  of  good  quality  will  give  results  equal  to  or  greater  than 
the  average  values  given. 

All  of  the  values  in  these  tables  were  obtained  from  the  " Ameri- 
can Civil  Engineers'  Pocket  Book,"  except  those  in  parenthesis 
which  were  obtained  from  other  sources. 


BUILDING  STONE 
STRENGTH  OF  BUILDING  STONE 


99 


Modulus  of 

Stone 

Compression, 
pounds  per 
square  inch 

Shear, 
pounds  per 
square  inch 

bending, 
pounds  per 
square  inch 

elasticity  in 
compression, 
pounds  per 
square  inch 

Granite  

15,000(18,000) 

2,000 

1,500 

7,000,000 

Sandstone  

8,000 

1,500 

1,200 

3,000,000 

Limestone  

6,000(8,500) 

1,000 

1,200 

7,000,000 

(8,000,000) 

Marble  

10,000 

1,400 

1,400 

8,000,000 

Slate  

15,000 

8,500 

14,000,000 

Marble  
Slate  

10,000                        1,400              1,400 
15,000                        8,500 

8,000,000 
14,000,000 

MECHANICAL  PROPERTIES  OF  BUILDING  STONE 

Stone 

Weight, 
pounds  per 
cubic  foot 

Specific 
gravity 

Per  cent  of 
absorption 

Coefficient 
of  expansion 
per  degree 
Fahrenheit 

Granite  

170(165) 
150(145) 
170(160) 
170(165) 
175 
185 

2.72(2.64) 
2.40(2.32) 
2.72(2.56) 
2.72(2.64) 
2.80 
2.96 

0.5  (0.7) 
3.0  (6.0) 
0.15(4.0) 
0.10(0.4) 
0.17(0.5) 

0.0000040 
0.0000055 
0.0000045 
0.0000045 
0.0000058 

Sandstone  
Limestone  
Marble       .  .  . 

Slate 

Trap  .  . 

CHAPTER  VII 

BRICK  AND  OTHER  CLAY  PRODUCTS 

A.  CLASSIFICATIONS  AND  DEFINITIONS 

129.  Classifications. — Common  brick  may  be  classified  accord- 
ing to  use ;  as  to  position  in  the  kiln  when  burned  (see  articles  on 
kilns  and  burning) ;  as  to  methods  of  manufacture ;  or  as  to  form 
and  shape.     Brick  and  clay  products  are  usually  classified  accord- 
ing to  their  uses. 

Classification  of  Brick  and  Clay  Products  According  to  Their 
Uses. 

1.  Building  Brick. — Used  for  ordinary  building  purposes. 

(a)  Common  building  brick. 

(b)  Face  brick,  pressed  or  re-pressed  brick. 

(c)  Enameled,  glazed,  and  ornamental  brick. 

(d)  Hollow  brick. 

(e)  Sand  lime  brick. 

(/)  Portland  cement  concrete  blocks  and  brick. 

2.  Paving  Brick  and  Block. — Vitrified  brick   or  blocks  used 
for  paving. 

3.  Fire  Brick. — Brick  made  so  that  they  can  withstand  a  high 
temperature. 

4.  Terra  Cotta. — Used  for  structural  purposes. 

(a)  Architectural  or  decorative. 

(b)  Blocks  and  lumber.     Used  for  structural  purposes. 

(c)  Hollow  building  blocks  and  fireproofing  material. 

5.  Building  Tile. — Used  for  structural  purposes. 

(a)  Roofing  tile. 

(b)  Wall  tile. 

(c)  Floor  tile. 

6.  Drain  Tile. — Porous,  non-vitrified,  unglazed  tile  used    for 
drainage  purposes. 

7.  Sewer    Tile. — Non-porous,    vitrified,    glazed   tile   used   for 
sewerage  purposes. 

130.  Definitions. — The    following    are    definitions    of    some 
of  the  different  kinds  of  brick.     Other  definitions  will  be  found  in 
the  articles  following. 

101 


102  MATERIALS  OF  CONSTRUCTION 

Clay  brick  are  made  by  molding,  drying,  and  burning  a  proper 
mixture  of  sand  and  clay. 

Sand  lime  brick  are  made  from  a  mixture  of  sand  and  lime. 

Terra  cotta  is  made  in  about  the  same  manner  as  ordinary  clay 
brick,  except  that  selected  clays,  that  will  burn  to  a  desirable  color 
with  a  slight  natural  glaze,  and  other  materials  are  used. 

Building  tile  are  made  in  about  the  same  manner  and  from 
about  the  same  materials  as  pressed  brick. 

Tile  and  pipes  are  made  by  burning  properly  selected  clay 
which  has  previously  been  molded  in  a  suitable  form. 

Re-pressed  brick  are  those  made  by  pressing  soft  or  stiff  mud 
brick  before  firing. 

Sewer  brick  are  hard  common  brick  or  No.  2  paving  brick  used 
for  sewers. 

Face  brick  are  usually  pressed  or  re-pressed  brick  that  are 
regular  in  shape  and  size  and  uniform  in  color.  They  are  used  for 
the  outside  of  walls  of  buildings. 

Feather  edge  brick  have  one  edge  thinner  than  the  other. 
They  are  used  in  arches. 

Compass  brick  have  one  edge  shorter  than  the  other.  They  are 
used  for  walls  with  curved  surfaces. 

Glazed  or  enameled  brick  have  one  face  glazed  or  enameled. 

B.  MANUFACTURE  OF  CLAY  BUILDING  BRICK 

131.  The  Clay. — Only  the  sedimentary  clays  are  sufficiently 
homogeneous,  fine,  and  plastic  enough  to  be  used  in  brick  making. 
These  clays  consist  principally  of  silicate  of  alumina  together  with 
a  little  lime,  magnesia,    and  iron  oxide.     An  excess  of  alumina 
makes  the  clay  very  plastic,  but  causes  it  to  shrink,  warp,  and 
crack  badly  in  drying,  and  also  makes  the  clay  very  hard  after 
burning.     Uncombined  silica,  if  not  in  excess  (not  over  25  per 
cent),  tends  to  preserve  the  form  of  the  brick,  but  an  excess 
destroys  the  cohesion  and  makes  the  brick  brittle  and  weak.     Iron 
oxide  makes  the  brick  hard  and  strong.     A  little  magnesia  tends 
to  decrease  the  shrinkage.     Silicate  of  lime  decreases  the  shrink- 
age, but  it  also  softens  the  brick  so  that  they  will  be  distorted  in 
burning.     Carbonate  of  lime  decomposes  in  burning  and  tends 
to  cause  the  brick  to  disintegrate. 

132.  Hand  Process  of  Making  Brick. — The  clay  is  first  cleaned 
of  all  pebbles,  dirt,  etc.,  by  washing,  after  which  it  is  mixed  with 


BRICK  AND  OTHER  CLAY  PRODUCTS  103 

a  moderate  amount  of  water.  To  reduce  the  clay  to  a  plastic 
mass,  it  is  usually  placed  in  a  pug  mill  and  then  the  proper 
amount  of  water  is  added.  The  pug  mill  consists,  essentially, 
of  a  cylinder  with  revolving  blades  inside  which  cut  up  and  mix 
the  material.  The  clay  may  be  made  plastic  by  hand  labor, 
but  this  process  is  very  laborious.  After  "pugging,"  the  plastic 
clay  is  pressed  into  the  molds  with  the  hands  and  tamped  hard. 
The  molds  are  sometimes  sprinkled  with  water,  but  they  are 
generally  sprinkled  with  sand  to  keep  the  clay  from  sticking  to 
them.  This  accounts  for  the  names  of  "slop"  and  "sand" 
molding. 

After  molding,  the  brick  are  dried  in  air,  often  for  several  weeks, 
before  they  are  fired  or  burned  in  a  kiln.     The  length  of  time 


FIG.  50. — Double  shaft  pug  mill.     (American  Clay  Machinery  Co.) 

required  for  drying  depends  on  the  weather  conditions  as  well  as 
on  the  composition  of  the  brick. 

If  the  brick  are  to  be  pressed,  this  must  be  done  before  they 
become  too  dry  and  hard.  The  press  is  a  simple  hand  machine  in 
which  the  brick  are  placed  between  plates  or  dies  and  then 
compressed  by  a  piston  operated  by  a  hand  lever. 

133.  Soft-mud  Machine  Process  of  Making  Brick.— The 
three  important  ways  of  making  machine-made  brick  are  the 
soft-mud  process,  the  stiff-mud  process,  and  the  pressed-brick 
process. 

In  the  soft-mud  process  the  clay  is  prepared  as  in  the  hand 
process  and  then  reduced  to  a  soft  mud  by  the  addition  of  water. 
The  process  of  manufacture  is  practically  the  same  as  the  hand 
process  except  that  most  of  the  work  is  done  by  machinery.  The 
molding  is  done  by  a  machine  which  presses  the  pugged  clay 
into  sanded  molds  by  means  of  a  plunger.  Gang  molds  are  used 


104 


MATERIALS  OF  CONSTRUCTION 


so  that  from  4  to  8  brick  are  molded  at  a  time.  Such  a  machine 
often  has  a  capacity  of  from  8,000  to  12,000  brick  per  day. 

The  soft-mud  brick  are  dried  in  the  same  way  as  the  hand-made 
brick,  except  that  sometimes  a  drying  house  is  used  to  accelerate 
the  drying. 

134.  Stiff-mud  Machine  Process  of  Making  Brick. — In 
the  stiff-mud  process  just  enough  water  is  added  to  the  clay  so 


FIG.  51. — Soft  mud  type  of  brick  machine  with  pug  mill.     (American  Clay 

Machinery   Co.) 

that  it  will  retain  its  shape  after  being  molded  under  a  moderate 
pressure.  The  consistency  of  this  clay  is  like  that  of  stiff  mud, 
hence  the  name. 

The.  molding  is  done  by  machines  which  are  either  of  the  auger 
or  plunger  types.  In  the  auger  type,  the  clay  is  forced  through  a 
die  by  means  of  an  auger  or  screw  working  in  a  cylinder;  while  in 
the  plunger  type  a  simple  piston  or  plunger  is  used  instead  of  the 
auger.  The  die  is  an  opening  equal  in  size  to  the  dimensions  of  an 
end  or  a  side  of  the  brick.  When  the  clay  comes  through  the  die, 
it  is  forced  out  on  a  long  table  where  it  is  cut  in  sections  the  size 
of  an  ordinary  brick.  If  the  cross-section  of  the  bar  of  clay  is  the 


BRICK  AND  OTHER  CLAY  PRODUCTS 


105 


same  as  the  end  of  a  brick,  the  brick  are  called  end  cut;  and  if 
the  section  is  the  same  as  the  side  of  a  brick,  they  are  called  side 
cut. 


FIG.  52. — Auger    type    of    brick    machine.     (American    Clay    Machinery    Co.) 


FIG.  53. — Plunger  type  of  brick  machine.     (American  Clay  Machinery  Co.) 


106 


MATERIALS  OF  CONSTRUCTION 


Often  the  brick  are  burned  without  any  preliminary  drying, 
but  this  is  not  good  practice  as  they  tend  to  crack  and  warp  in 
the  burning.  It  is  better  first  to  dry  the  brick  for  a  time  in  air, 
or  place  them  in  a  drying  house  where  the  drying  is  accelerated 
by  means  of  steam  pipes  or  hot  air. 

135.  Pressed -brick  Machine  Process  of  Making  Brick. — In 
the  pressed-brick  process,  the  clay  is  either  used  dry  (containing 
less  than  7  per  cent  of  water)  or  semi-dry  (containing  more  than 
7  per  cent  of  water  but  not  so  much  water  as  the  clay  used  in  the 
stiff  mud  process).  The  clay  is  ground  to  the  fineness  of  flour 


FIG.  54. — Side  cut  brick  table  for  plunger  machine.     (American  Clay  Machinery 

Co.) 

before  being  delivered  to  the  brick  machine.  This  machine 
feeds  the  clay  into  the  molds  and  then  compresses  it  (under  an 
enormous  pressure)  by  means  of  plungers. 

These  brick  require  less  drying  than  the  other  kinds,  and, 
consequently,  are  often  burned  without  any  preliminary  drying. 

Pressed  brick  are  very  compact  and  strong,  but  they  are 
thought  to  be  less  durable  than  those  brick  in  which  more  water 
is  used  during  the  making. 

136.  Brick  Kilns. — Brick  kilns  may  be  classified  as  intermit- 
tent or  continuous  kilns,  according  to  their  method  of  operation. 
The  intermittent  kilns  are  subdivided  into  updraught,  down- 
draught,  and  up-and-down-draught  kilns. 

The  old  style  updraught  kiln  is  usually  just  a  pile  of  brick 
about  20  or  30  ft.  wide,  30  or  40  ft.  long,  and  10  or  15  ft.  high. 
The  brick  are  so  piled  as  to  form  a  number  of  arched  openings 
extending  through  the  pile.  The  sides  of  the  pile  are  often 
plastered  with  mud  and  the  top  covered  with  dirt  and  some- 


BRICK  AND  OTHER  CLAY  PRODUCTS 


107 


times  roofed  so  as  to  keep  in  the  heat.  The  more  modern  type 
of  updraught  kilns  are  built  with  permanent  side  walls.  This 
updraught  kiln  is  not  so  economical  as  the  other  types,  as  many 


FIG.  55. — Dry    clay    brick    press   machine.     (American    Clay   Machinery    Co.) 


FIG.  56. — Hundred  and  ten  chamber  Haigh  continuous  kiln.     Five  fires. 
(American  Clay  Machinery  Co.) 

(about  half)  of  the  brick  have  to  be  discarded  on  account  of 
over-and-under  burning. 

A  downdraught  kiln  has  permanent  walls,  a  floor,  a  tight  roof, 
chimney,  and  furnaces.  The  floor  has  openings  connecting  with 
flues  leading  to  the  chimney.  The  heat  is  generated  in  outside 
ovens  and  enters  the  kiln  in  such  a  way  that  it  reaches  the  top  of 
the  brick  piles  first  and  passes  down  through  the  piles  to  the  open- 


108  MATERIALS  OF  CONSTRUCTION 

ings  in  the  floor,  and  then  through  the  flues  to  the  chimney. 
This  kiln  burns  the  brick  very  evenly  and  only  a  few  of  them  have 
to  be  discarded  on  account  of  over-or  under-burning. 

The  up-and-down-draught  kiln  is  so  arranged  with  two  sets  of 
furnaces  that  the  heat  from  one  furnace  can  be  made  to  pass 
down  through  the  brick  while  the  heat  from  the  other  furnace  can 
be  made  to  pass  up  through  rthe  brick  before  passing  to  the 
chimney.  This  type  of  kiln  burns  the  brick  very  uniformly. 

Continuous  kilns  are  of  many  types,  but  they  all  consist 
essentially  of  a  series  of  chambers  with  flues  between  them  and 
also  between  each  chamber  and  the  stack.  When  one  chamber  is 
fired,  the  heat  can  be  made  to  traverse  several  other  chambers 
before  going  to  the  chimney,  thus  preheating  the  brick  in  those 
chambers  and  securing  an  economy  of  fuel.  Only  one  chamber 
needs  to  be  out  of  operation  at  any  one  time  because  of  the 
changing  of  the  piles  of  brick. 

137.  Burning  the  Brick. — The  fuel  used  usually  depends  upon 
local  conditions.     The  furnaces  in  the  kilns  may  be  designed  to 
use  wood,  coal,  or  gas.     Wood  is  usually  used  in  the  old-style 
updraught  kilns  where  the  fires  are  built  in  the  archways. 

The  brick  are  first  subjected  to  a  fire  giving  a  moderate  tem- 
perature until  the  moisture  is  expelled.  Then  the  temperature 
is  increased  until  the  brick  in  the  hottest  part  of  the  kiln  are  at  a 
white  heat,  and  the  other  bricks  at  a  red  heat.  The  fire  is  kept 
at  this  temperature  until  the  burning  of  the  brick  is  complete. 
Ordinary  burning  requires  from  6  to  15  days. 

When  the  burning  is  completed,  the  fires  are  stopped  and  all 
of  the  openings  are  closed  so  as  to  exclude  any  cool  currents  of 
air.  Then  the  kiln  and  the  brick  are  allowed  to  cool  slowly  for 
several  days  before  the  kiln  is  opened  and  the  brick  removed. 
This  slow  cooling  " anneals"  the  brick  and  makes  them  tough. 

The  brick  nearest  the  fire  are  usually  overburned  and  are 
called  arch  or  clinker  brick.  The  brick  in  the  coolest  part  of  the 
kiln  are  usually  underburned  and  these  brick  are  called  salmon 
or  soft  brick.  All  of  the  other  brick  in  the  kiln,  which  are 
properly  burned,  are  called  body,  cherry,  or  hard  brick  and  are 
the  brick  that  are  valuable  for  building  purposes. 

C.  MANUFACTURE  OF  OTHER  BRICK 

138.  Manufacture   of  Paving  Brick. — These   brick   are  used 
for  paving  purposes  and  should  be  hard,  tough,  and  non-absorp- 


BRICK  AND  OTHER  CLAY  PRODUCTS  109 

live.  Their  manufacture  differs  from  that  of  ordinary  clay  brick 
because  they  are  burned  at  a  much  higher  temperature  (high 
enough  to  vitrify  the  brick)  and  also  because  the  selection  of  a 
suitable  clay  is  more  limited. 

Surface  clays,  impure  fireclays,  and  shales  have  been  used  in 
the  manufacture  of  paving  brick,  but  the  shales  are  the  best  and 
most  used  material  at  the  present  time.  These  clays  occur  in 
large  bodies  and  are  rocklike,  but  they  are  easily  reduced  to  a 
powder.  They  are  impure  and  have  a  range  of  vitrification 
often  extending  over  300  degrees  Fahrenheit.  The  shale  banks 
are  usually  worked  with  steam  shovels. 

When  the  clay  arrives  at  the  factory,  it  is  crushed  to  a  powder 
by  grinding  machinery  and  delivered  to  a  pug  mill  where  just 
enough  water  is  mixed  with  the  clay  to  make  a  stift  mud.  The 
brick  are  molded  as  in  the  stiff-mud  process  and  are  repressed 
immediately  after  molding.  This  repressing  makes  the  brick 
more  uniform,  rounds  off  the  corners,  and  makes  lugs  on  the 
sides  so  that  the  brick  will  be  separated  a  little  from  each  other 
when  laid  in  a  pavement.  Sometimes  the  brick  are  wire  cut  and 
not  repressed.  This  kind  is  called  "wire  cut  lug  brick."  The 
brick  are  usually  dried  in  a  dry  house  before  they  are  burned. 

Paving  brick  are  burned  in  a  down-draught  or  a  continuous 
kiln.  The  time  required  for  burning  is  about  ten  days.  The 
heat  necessary  is  a  bright  cherry  heat  (from  1,500  to  2,000  degrees 
Fahrenheit)  for  shales,  while  only  a  red  heat  is  reached  in  burning 
common-clay  building  brick.  Different  clays  require  different 
temperatures.  After  the  brick  are  thoroughly  burned,  the  kiln 
is  tightly  closed  and  allowed  to  cool  slowly  for  several  days.  This 
tends  to  anneal  the  brick  and  make  them  more  tough.  Upon 
emptying  the  kiln  the  brick  should  be  sorted  into  different  classes. 
With  shales,  about  70  or  80  per  cent  of  No.  1  paving  brick  are 
obtained. 

139.  Manufacture  of  Firebrick. — Firebrick  may  be  classified 
as  follows: 

1.  Add  Brick. — 

(a)  Fireclay  brick. 
(6)  Silica  brick. 
(c)  Canister  brick 

2.  Basic  Brick. — 

(a)  Magnesia  brick. 
(6)  Bauxite  brick. 


110  MATERIALS  OF  CONSTRUCTION 

3.  Neutral  Brick  — 
(a)  Chromite  brick. 

Fireclay  brick  are  made  of  ordinary  fireclay  mixed  with  a  little 
flint  clay,  sand,  burned  fireclay,  or  other  refractory  material  to 
prevent  too  great  a  shrinkage  in  burning  and  drying.  The 
molding  and  drying  may  be  done  by  any  of  the  ordinary  ways, 
while  the  firing  is  usually  done  in  a  down-draught  or  continuous 
kiln.  A  temperature  of  from  2,500  to  3,500  degrees  Fahrenheit 
is  required  in  the  burning.  The  cooling  should,  be  fast  until 
2,500  degrees  Fahrenheit  is  reached,  and  then  it  should  be  slow. 

Silica  firebrick  are  made  of  silica  sand  mixed  with  a  little  lime 
(about  2  per  cent)  to  act  as  a  binder.  These  firebrick  are  usually 
molded  by  hand,  dried  in  a  drying  room,  and  fired  in  a  down- 
draught  kiln.  The  temperature  required  is  from  2,600  to  3,200 
degrees  Fahrenheit.  The  cooling  must  be  done  very  slowly  and 
uniformly.  A  very  good  grade  of  silica  firebrick  can  be  made  by 
the  process  used  in  making  sand  lime  brick. 

Ganister  brick  are  made  from  ganister  rock,  which  is  a  dense 
siliceous  sandstone  containing  about  10  per  cent  of  clay.  The 
process  of  manufacture  is  the  same  as  that  for  silica  brick,  except 
that  no  lime  is  added. 

Magnesia  brick  are  made  from  a  mixture  of  caustic  magnesia 
and  sintered  magnesia  with  a  little  iron  oxide  for  a  flux.  The 
materials  are  ground  and  mixed;  water  is  added  in  the  pug  mill; 
and  the  brick  are  molded  under  a  heavy  pressure.  They  must 
be  carefully  dried  before  being  fired.  The  temperature  required 
is  from  3,300  to  3,450  degrees  Fahrenheit.  These  brick  warp 
and  shrink  badly. 

Bauxite  brick  are  made  by  mixing  ground  bauxite  (containing 
more  than  85  per  cent  of  A12O3)  with  about  25  per  cent  of  clay 
in  a  pug  mill;  adding  water;  and  molding  by  hand  or  with  a  stiff 
mud  machine.  The  brick  are  burned  at  a  temperature  of  about 
2,800  degrees  Fahrenheit.  They  are  weak  and  shrink  greatly 
in  drying  and  burning. 

Chromite  brick  are  made  from  a  mixture  of  chrome  iron  ore 
and  fire  clay  or  bauxite.  The  mixture  contains  about  50  per 
cent  of  chromium  ore,  30  per  cent  of  ferrous  oxide,  and  20  per 
cent  of  alumina  and  silica.  The  materials  are  ground,  mixed, 
and  molded  under  heavy  pressure,  as  in  the  case  of  the 
silica  brick.  The  burning  temperature  is  about  3,000  degrees 
Fahrenheit. 


BRICK  AND  OTHER  CLAY  PRODUCTS  111 

140.  Manufacture    of    Sand-lime    Brick. — Sand-lime    brick 
consist  of  a  mass  of  sand  cemented  together  with  lime.     There 
are  several  classes  of  these  brick,  but  only  one  is  of  importance 
as  a  structural  material.     This  class  of  brick  is  made  of  a  mixture 
of  sand  and  lime  which  is  molded  in  a  press  and  then  subjected 
to  steam  under  pressure. 

The  sand  used  should  be  well  graded  so  as  to  have  a  low 
percentage  of  voids.  The  binding  action  between  the  sand  and 
the  lime  is  better  with  fine  sand;  hence,  the  sand  should  not  be 
too  coarse.  A  well-graded  mixture  has  been  found  to  have  a  low 
percentage  of  absorption.  The  sand  should  contain  a  sufficient 
proportion  of  fine  quartz  sand  and  it  should  also  be  clean  and  dry 
when  mixed  with  the  lime. 

The  lime  used  may  be  either  a  high-calcium  or  a  dolomitic 
lime,  but  the  former  is  preferable.  The  lime  should  be  hydrated 
or  slaked  either  before  or  at  the  time  of  mixing  with  the  sand. 
The  amount  of  lime  varies  from  5  to  10  per  cent  of  the  sand. 

The  thorough  mixing  of  the  sand,  lime,  and  water  is  the  most 
important  part  of  the  process  of  manufacture.  It  is  preferable 
to  mix  the  dry  sand  and  the  dry  hydrated  lime  thoroughly  and 
then  add  the  water  and  mix  again. 

The  mixture  is  molded  into  brick  in  the  same  manner  as  in  the 
pressed-brick  (dry  clay)  process.  The  pressure  exerted  by  the 
machine  on  the  mixture  in  the  mold  is  about  15,000  Ib.  per 
square  inch. 

The  brick  are  hardened  by  placing  them  in  a  closed  hardening 
cylinder  and  subjecting  them  to  steam  under  a -pressure  of  about 
125  Ib .  per  square  inch.  The  length  of  time  required  for  harden- 
ing at  this  pressure  is  about  10  hours. 

D.  OTHER  CLAY  PRODUCTS 

141.  Terra  Cotta. — Terra  cotta  is  made  in  about  the  same  way 
as  ordinary  clay  brick,  but  it  requires  a  carefully  selected  clay 
that  will  burn  to  a  desirable  color  with  a  slight  natural  glaze. 
Usually,  no  single  clay  is  used,  but  a  mixture  is  made  of  several 
clays  in  order  to  obtain  the  desired  effect. 

Decorative  terra  cotta  is  usually  made  by  hand  molding  and 
then  dried  and  burned.  Very  great  care  must  be  taken  to 
prevent  distortion  and  discoloration  during  firing. 

Terra  cotta  lumber  and  building  blocks,  which  are  used  for 


112  MATERIALS  OF  CONSTRUCTION 

structural  purposes,  are  usually  made  of  a  mixture  of  terra  cotta 
clays  and  finely  cut  straw  or  sawdust.  The  method  of  manu- 
facture is  like  that  of  the  stiff-mud  process,  except  that  special 
care  must  be  taken  to  prevent  distortion  and  unequal  heating  in 
firing.  The  burning  temperature  is  high  enough  to  burn  out  all 
of  the  straw  and  sawdust  and  leave  a  light  porous  material. 
About  all  of  the  terra  cotta  lumber  is  hollow  in  construction 
with  outside  walls  about  1  in.  thick  and  partition  walls  about 
%  in.  thick. 

Terra  cotta  building  blocks  and  fireproofing  are  the  same  as 
terra  cotta  lumber,  except  that  no  straw  or  sawdust  is  used  and 
the  firing  temperature  is  high  enough  to  vitrify  the  clay. 

142.  Building  Tile. — Building  tile  may  be  divided  according 
to  use  into  roofing,  wall,  and  floor  tile. 

Roofing  tile  are  made  in  the  same  way  as  pressed  brick,  except 
that  the  flat  forms  may  be  made  by  the  stiff-mud  process. 
The  clay  is  selected  with  greater  care  than  in  the  case  of 
ordinary  brick.  The  shape  of  the  tile  may  be  flat,  curved,  or 
interlocking. 

There  are  two  kinds  of  wall  tile  called  dust-pressed  tile  and 
plastic  tile.  The  clay  used  in  making  dust-pressed  wall  tile  may 
be  a  fireclay,  shale  clay,  or  a  mixture  of  clays.  The  materials  are 
ground,  mixed,  and  then  made  up  to  the  consistency  of  thin 
cream  and  strained  through  a  silk  screen.  The  water  is  drained 
off,  the  material  dried,  crushed  to  a  powder,  and  slightly  moisten- 
ed by  steam.  The  molding  is  done  in  a  dry  press  and  the  tile  are 
burned  in  fireclay -boxes  to  keep  the  tile  from  coming  in  contact 
with  the  flames.  After  the  first  burning,  a  glaze  may  be  applied 
and  coloring  matter  added  and  the  tile  burned  a  second  time  to 
fuse  the  glaze.  Plastic  tile  are  made  in  the  same  way  as  dust- 
pressed  tile,  except  that  a  mixture  of  soft  clay  and  burned  clay 
is  used  and  the  molding  is  done  immediately  after  the  mixing 
and  the  addition  of  the  water.  Most  wall  tile  are  dust-pressed 
tile. 

An  inferior  product  of  building  tile  (and  some  kinds  of  terra 
cotta)  is  made  from  a  finely  divided  clay  similar  to  that  used  for 
ordinary  clay  brick.  The  stiff-mud  process  is  used,  and  the  tile 
are  wire  cut.  The  burning  is  the  same  as  that  given  to  ordinary 
clay  building  brick  and  is  usually  done  in  a  down-draught 
kiln. 

143.  Drain  Tile. — Drain  tile  are  made  from  a  red  burning  clay 


BRICK  AND  OTHER  CLAY  PRODUCTS 


113 


(shale  clay),  fireclay,  surface  clay,  or  from  a  mixture  of  clays  like 
those  used  in  making  terra  cotta  lumber.  The  tile  are  made  by 
the  stiff  mud  process,  and  the  burning  is  done  at  a  temperature 
that  aids  in  the  production  of  a  strong  porous  product  that  is  not 
vitrified  or  glazed. 

The  tile  may  be  classified  according  to  the  materials  from 
which  they  are  made,  according  to  their  use,  or  according  to  their 


FULL-  $-HALF- JAMB  -TILE 


FIG.  57. — Standard  wall  and  jamb  tile. 

general  physical  properties. 

Drain  tile  are  used  for  draining  water  from  fields,  roads, 
ditches,  etc.,  and  they  must  be  porous  so  that  the  water  can  pass 
from  the  soil  through  the  walls  of  the  tile  into  the  interior  of  the 
pipe. 

144.  Sewer  Pipe. — Sewer  pipe  is  made  from  such  clays  as  will 
produce  a  non-porous  tile  with  a  low  percentage  of  absorption. 


114  MATERIALS  OF  CONSTRUCTION 

The  stiff-mud  process  of  manufacture  is  used  for  ordinary  pipes, 
and  the  dry-press  process  for  those  pipes  having  sockets  at  the 
end  or  which  are  of  some  special  shape.  The  pipe  is  dried  in  a 
steam  chamber  and  then  burned  in  a  down-draught  kiln.  When 
the  temperature  reaches  about  2,100  degrees  Fahrenheit,  common 
salt  is  thrown  on  the  kiln  fires.  The  sodium  vapors  from  the 
salt  combine  with  the  clay  and  form  a  hard  glaze  on  the  surface 
of  the  pipe  and  thus  make  the  pipe  very  non-absorptive.  Sewer 
pipe  may  be  classified  in  the  same  ways  as  drain  tile. 

As  sewer  pipes  are  used  for  carrying  sewage,  it  is  important 
that  they  be  non-porous  and  non-absorptive  and  that  they  have 
good  tight  joints. 

E.  PROPERTIES  OF  BRICK  AND  OTHER  CLAY  PRODUCTS 

145.  General  Properties  of  Brick.     Requisites  of  Good  Brick. — 
A  good  brick  should  have  plane  faces,  parallel  sides,  sharp  edges 
and  angles,  a  fine,  compact,  uniform  texture,  and  it  should  contain 
no  cracks,  fissures,  air  bubbles,  pebbles,  lumps  of  lime,  etc.     A 
brick  should  give  a  clear  ringing  sound  when  struck  with  the 
hammer  or  another  brick.     A  paving  brick  should  be  hard  and 
tough  to  resist  wear  and  impact,  and  it  should  be  free  from 
laminations  or  seams  so  that  it  will  wear  uniformly  in  a  pavement. 

Common  clay  building  brick  of  good  quality  weigh  about  125 
Ib.  per  cubic  foot;  face  or  pressed  brick  about  135  Ib.  per  cubic 
foot;  sand-lime  brick  about  115  Ib.  per  cubic  foot;  and  paving 
brick  about  150  Ib.  per  cubic  foot. 

The  sizes  of  brick  vary  in  different  countries  and  different 
localities.  The  standard  size  for  common  brick  in  America  is 
8J4  by  4  by  2J4  in.,  and  for  paving  brick  8^  by  4  by  2^  in. 
Paving  blocks  are  about  3  by  4  by  9  in.  in  size. 

146.  Absorption  of  Brick  and   Building  Tile. — Formerly,   it 
was  thought  that  if  a  brick  would  absorb  much  water  it  was  not 
so  durable  as  other  brick  and  was  more  liable  to  destruction  by 
frost,  but    this  opinion    has  not    been    substantiated    by  tests. 
The  absorptive  power  of  a  brick  depends  somewhat  on  its  compact- 
ness but  more  on  the  chemical  composition  of  the  clay.     There 
appears  to  be  no  close  relation  between  the  absorptive  power  and  the 
strength  and  durability  of  the  brick.     The  following  table  shows 
the  approximate  range  of  absorption  in  different  kinds  of  brick 
which  have  been  immersed  in  water  for  48  hours. 


BRICK  AND  OTHER  CLAY  PRODUCTS  115 

ABSORPTION  OF  BRICK  AND  BUILDING  TILE 
Percentages  are  based  on  the  weight  of  the  dry  brick 

KIND  OP  BBICK  PERCENTAGE  OP  ABSORPTION 

Common  clay  building  brick 12  to  18 

Pressed  or  face  brick :  . .  .  6  to  12 

Sand-lime  brick 12  to  15 

Paving  brick  and  blocks 1  to    3 

Fireclay  brick 8  to  12 

Unglazed  terra  cotta  blocks  and  building  tiles . .  10  to  15 

147.  Compressive  Strength  of  Brick  and  Building  Tile.— The 
compression  test  of  brick  is  only  of  relative  value  for  comparing 
different  kinds  of  brick,  because,  when  a  brick  is  used  in  masonry, 
its  crushing  strength  is  not  of  much  importance  unless  the  mortar 
used  with  the  brick  has  nearly  the  same  strength.     Ordinary 
mortar   used    in   brick  masonry  is  generally  very  much  weaker 
than  the  brick.     Soaking  a  brick  in  water  tends  to  decrease  its 
strength  in  compression.     The  following  table  will  give  an  idea 
of  the  average  compressive  strength  of  good  brick: 

COMPRESSIVE  STRENGTH  OF  BRICK  AND  BUILDING  TILE 

STRENGTH  IN  POUNDS 

KIND  OF  BRICK  PER  SQUARE  INCH 

Average  good  clay  building  brick 4 , 000 

Pressed  brick 8,000 

Sand-lime  brick 3,000  to  4,000 

Paving  brick  and  blocks 10 , 000 

Fireclay  brick 3,000  to  6,000 

Terra  cotta  blocks  and  building  tile 4,000 

Architectural  terra  cotta 3,000 

148.  Transverse  Strength  of  Brick  and  Building  Tile.— The 
transverse  tests  are  easy  to  make  and  they  give  results  that  are 
definite  and  which  furnish  the  best  indications  of  the  quality  of 
the  brick.     Transverse  tests  afford  an  indication  of  the  toughness 
and  also  of  the  ability  of  the  brick  to  resist  ordinary  failures  in 
brick  walls.     In  masonry  walls  the  mortar  usually  fails  first 
and  squeezes  out,  thus  setting  up  bending  stresses  in  the  brick 
which  cause  them  to  fail.     The  appearance  of  the  fractured 
surface  is  a  good  indication  of  the  care  with  which  the  brick 
have  been  made.     The  following  table  gives  an  average  range 
of  values: 


116  MATERIALS  OF  CONSTRUCTION 

CROSS-BENDING  STRENGTH  OF  BRICK  AND  BUILDING  TILE 

MODULUS  OP  RUPTURE 

IN  POUNDS 
KIND  or  BRICK  PER  SQUARE  INCH 

Common  clay  building  brick 500  to  1 , 000 

Pressed  or  face  brick 600  to  1 , 200 

Sand-lime  brick 300  to      600 

Paving  brick  and  blocks 1 , 500  to  2 , 500 

Fireclay  brick 300  to      600 

Unglazed  terra  cotta  blocks  and  building 

tile 500  to  1,000 

149.  Shearing   Strength   of   Brick   and   Building   Tile.— The 

shearing  strength  of  brick  is  of  but  little  importance  and  the  tests 
are  very  hard  to  make  properly.  Tests  made  at  the  Watertown 
Arsenal  gave  the  following  values.  Results  for  terra  cotta  and 
building  tile  were  taken  from  another  source. 

SHEARING  STRENGTH  OF  BRICK  AND  BUILDING  TILE 

STRENGTH  IN  POUNDS 

KIND  OP  BRICK  PER  SQUARE  INCH 

Common  clay  building  brick 1 , 000  to  1 , 500 

Pressed  or  face  brick 800  to  1 , 200 

Sand-lime  brick 500  to  1 , 000 

Paving  brick  and  blocks 1 , 200  to  1 , 800 

Fireclay  brick 500  to  1 , 000 

Unglazed  terra  cotta  blocks  and  building 

tile 600  to  1 , 200 

150.  Modulus  of  Elasticity  of  Brick  and  Building  Tile. — The 

modulus  of  elasticity  of  brick  in  compression  is  not  a  constant 
quantity  because  the  stress  strain  curve  in  compression  is  a 
curved  line  throughout  its  length,  similar  to  the  stress  strain 
curves  for  concretes  and  mortars.  The  following  are  average 
values  of  the  modulus  of  elasticity  in  compression  for  loads  not 
exceeding  one-fourth  of  the  ultimate  strength. 

MODULUS  OF  ELASTICITY  IN  COMPRESSION  OF  BRICK  AND  BUILDING  TILE 

MODULUS  op  ELASTICITY 

IN  POUNDS 
KIND  OP  BRICK  PSR  SQUARE  INCH 

Common  clay  building  brick 1 , 500 , 000  to  2 , 500 , 000 

Pressed  or  face  brick 2 , 000 , 000  to  3 , 000 , 000 

Sand-lime  brick 800,000  to  1 ,200,000 

Paving  brick  and  blocks 4,000,000  to  8,000,000 

Unglazed     terra    cotta    blocks     and 

building  tile 1,500,000  to  3,000,000 


BRICK  AND  OTHER  CLAY  PRODUCTS 


117 


151.  Properties  of  Drain  Tile.  Requisites. — All  drain  tile 
should  be  free  from  visible  grains  of  caustic  lime,  iron  pyrites, 
or  other  minerals  which  are  known  to  cause  slaking  or  the  dis- 
integrating of  the  tile.  The  drain  tile  should  be  of  the  proper 
shape,  diameter,  and  length;  uniform  in  structure,  smooth  on 
the  inside,  free  from  cracks  and  checks  that  would  appreciably 
lower  the  strength ;  properly  burned ;  and  should  give  a  clear  ring 
when  stood  on  end  and  tapped  with  a  light  hammer. 

Drain  tile  are  divided  into  three  classes  (farm  drain  tile, 
standard  drain  tile,  and  extra  quality  drain  tile)  according  to 
quality  and  use.  The  physical  tests  include  strength  and  ab- 
sorption tests  and  sometimes  freezing  tests.  Any  good  drain  tile 
should  easily  pass  the  following  minimum  requirements  for 
strength  and  not  absorb  more  water  than  the  maximum  values 
given  below: 

MINIMUM  REQUIREMENTS  FOR  STRENGTH  OF  DRAIN  TILE 


Internal 
diameter  of 
pipe,  inches 

Average  supporting  strength  in  pounds  per  lineal  foot 

Farm  drain 
tile 

Standard  drain 
tile 

Extra  quality 
drain  tile 

4 
8 
12 
16 
20 
24 
30 
36 
42 

800 
800 
800 
1,000 

,200 
,200 
,200 
,300 
,500 
,700 
2,000 
2,300 
2,600 

1,600 
1,600 
1,600 
1,700 
2,000 
2,400 
3,000 
3,600 
4,200 

MAXIMUM  ALLOWABLE  ABSORPTION  FOR  DRAIN  TILE 
Standard  boiling  test.     All  values  are  percentages  of  the  dry  weight. 


Materials  used  in  making 

Farm  drain 
tile,  per  cent 

Standard  drain 
tile,  per  cent 

Extra  quality 
drain  tile, 
per  cent 

Shale  and  fireclay  tile  
Surface  clay  tile 

11 
14 

9 
13 

7 
11 

Concrete  tile 

12 

11 

10 

118 


MATERIALS  OF  CONSTRUCTION 


152.  Properties  of  Sewer  Pipes.  Requisites. — Sewer  pipes 
should  be  of  the  hub  and  spigot  type  preferably,  properly  made 
and  burned,  vitrified,  and  salt  glazed.  All  pipes  should  be  of 
proper  dimensions,  straight,  sound,  well  glazed  throughout, 
smooth  on  the  inside,  free  from  blisters,  lumps,  or  flakes  which  are 
broken  or  are  larger  than  allowed  by  the  specifications,  and  free 
from  fire  checks  and  cracks  extending  through  the  thickness  of 
the -pipe.  The  thickness  of  the  walls  should  be  at  least  j^2  of 
the  inside  diameter. 

The  thickness  of  the  walls  of  ordinary  sewer  pipes  is  less  than 
y\2  of  the  inside  diameter,  while  that  of  " double  strength" 
pipes  is  equal  to  Y\i  of  the  inside  diameter. 

The  following  table  gives  the  minimum  strength  requirements 
of  the  Tentative  (Proposed)  Specifications  for  Sewer  Pipes  of 
the  American  Society  for  Testing  Materials,  the  Specifications 
of  the  City  of  Brooklyn  for  Sewer  Pipes  and  the  results  of  strength 
tests  made  in  that  city.  These  results  are  higher  than  would 
ordinarily  be  expected  from  tests  on  ordinary  salt-glazed  and 
vitrified-clay  sewer  pipes.  Any  good  sewer  pipe  should  be  able 
to  pass  the  A.  S.  T.  M.  specifications. 

The  requirements  for  the  specification  for  absorption  have  not 
yet  been  decided  upon.  However,  good  salt-glazed  vitrified-clay 
sewer  pipes  should  not  absorb  more  than  3  per  cent  of  water  on 
the  average  or  more  than  5  per  cent  in  any  individual  case. 

MINIMUM  STRENGTH  REQUIREMENTS  AND  RESULTS  OF  TESTS  OF  SEWER 

PIPES 
Average  supporting  strengths  in  pounds  per  lineal  foot. 


Inside  diam- 
eter, inches 

A.  S.  T.  M.  tenta- 
tive specifications 

Brooklyn 
specifications 

Brooklyn 

test  results 

6 

1,430 

1,000 

4,275 

8 

1,430 

9 

1,050 

3  983 

10 

1,570 

12 

1,710 

1,150 

4,696 

15 

1,960 

1  ,  300 

5,046 

18 

2,200 

1,450 

6,311 

21 

2,590 

24 

3,070 

2,000 

9,866 

30 

3,690 

36 

4,400 

42 

5,030 

CHAPTER  VIII 


STONE  AND  BRICK  MASONRY 

A.  STONE  MASONRY 

153.  Stone  Masonry  in  General. — Stone  masonry  includes  all 
masonry  in  which  stone  form  the  most  important  part.  When 
mortar  is  used  with  stone  masonry,  it  is  called  "  wet "  or  "  mortar  " 
masonry.  When  no  mortar  is  used,  it  is  called  "dry"  masonry. 

Stone  masonry  is  one  of  the  oldest  forms  of  construction  known 
to  mankind.  It  has  been  used  by  practically  all  peoples  through- 
out all  ages  and  in  all  countries  where  the  stones  could  be  readily 
obtained . 

Structures  made  of  stone  masonry  are  very  durable  and  some  of 
them  have  been  in  use  for  more  than  a  hundred  years. 


Coping 


Section  A- A 


FIG.  58. — Range  masonry.     Sketch  showing  arrangement  and  names  of  parts. 

Stone  masonry  is  used  for  various  buildings,  retaining  walls, 
dams,  piers,  abutments,  arches,  bridges,  paving,  culverts,  founda- 
tions, etc. 

154.  Definitions. — The  following  are  definitions  of  some  of  the 
terms  often  used  in  connection  with  stone  (and  brick)  masonry. 
Other  definitions  will  be  found  in  the  articles  following. 

119 


120  MATERIALS  OF  CONSTRUCTION 

Batter  is  the  slope  of  the  surface  of  the  wall. 

Coping  is  a  course  of  heavy  stones  laid  on  top  of  a  wall  to 
protect  it. 

Course  is  a  horizontal  layer  of  stones  in  a  wall. 

Cramps  are  bars  of  iron  or  steel  having  their  ends  bent  at 
right  angles  to  the  body  of  the  bar.  These  ends  enter  holes  in 
adjacent  stones  to  keep  the  stones  from  separating. 

Dowels  are  short  straight  bars  of  iron  or  steel  which  enter  holes 
in  adjacent  stones  which  are  above  each  other  to  prevent  one 
stone  from  slipping  on  the  other. 

Face  is  the  front  surface  of  the  wall. 

Back  is  the  rear  surface  of  the  wall. 

Facing  is  the  stone  or  other  material  which  forms  the  face  of 
the  wall. 

Filling  is  the  material  in  the  interior  of  the  wall. 

Backing  is  the  material  forming  the  back  of  the  wall. 

Quoin  is  a  stone  laid  in  the  corner  of  a  wall. 

155.  Classification  of  Stone  Masonry. — The  following  is  a 
classification  of  stone  masonry: 

A.  Dry  Masonry 

1.  Slope  wall  masonry  is  a  thin  layer  of  stone,  or  an  inclined 
wall  of  stone,  built  against  slopes  of  embankments,  excavations, 
river  banks,  etc.,  to  protect  them  from  rain,  waves,  or  weather. 

2.  Stone  paving  is  a  dry  stone  masonry  used  for  paving  the 
floors  or  ends  of  culverts  and  similar  structures. 

3.  Riprap  is  stone  of  any  shape  or  size  placed  on  river  banks 
or  around  piers,  abutments,  etc.,  to  prevent  wash  and  scour  by 
the  water.     The  stone  may  be  dumped  in  place,  but  they  are 
more  effective  if  arranged  by  hand. 

B.  Wet  or  Mortar  Masonry 

1.  Rubble  masonry   which  is  composed  of  rough  unsquared 
stone. 

(a)  Coursed  rubble  in  which  the  stone  are  leveled  off  at 
specified  heights  to  an  approximately  level  surface. 

(6)  Uncoursed  rubble  which  is  laid  without  any  attempt  at 
regular  courses. 

2.  Squared  stone  masonry  is  masonry  in  which  the  stone  are 
roughly  squared  and  roughly  dressed  on  beds  and  joints.     The 


STONE  AND  BRICK  MASONRY 


121 


thickness  of  the  mortar  required  in  the  joints  is  more  than  %  in. 
This  class  may  be  subdivided  according  to  the  facing  of  the 
stone  into: 

(a)  Pitched  faced  masonry. 

(6)  Quarry  faced  masonry. 

Or  this  class  may  be  divided  according  to  the  manner  in 
which  the  stone  are  laid: 

(a)  Range  work  which  is  laid  in  courses. 

(6)  Broken  range  which  is  laid  in  broken  courses. 

(c)  Random  masonry  which  is  laid  with  no  attempt  at 
courses. 


"••59 

UNOOURSID RUBBLE 


RUBBLE 


Uf»f  ED  RUBBLE 


=55:3 

-V- 

^ 

Mi     i 

rM 

-    1       1 

1      1 

I       l 

— 

1       1    1     1 

ASHLAR 


FIGS.  59-67. — Stone  masonry. 

3.  Cut  stone  or  ashlar  masonry  which  is  composed  of  any  of 
the  kinds  of  cut  stone  where  the  required  thickness  of  the  mortar 
joints  is  less  than  J^  in. 

This  class  is  usually  subdivided  as  follows: 
(a)  Coursed   ashlar    in   which  the  courses  are  continuous 
(range  work). 


122  MATERIALS  OF  CONSTRUCTION 

(b)  Broken  ashlar  in  which  the  courses  are  broken  and  not 
continuous  (broken  range). 

156.  Mortar  for  Stone  Masonry. — Mortar  for  stone  masonry 
has  three  functions:   (1)  to  form  a  bed  or  cushion  for  the  stone 
so  as  to  distribute  the  pressure  uniformly;  (2)  to  bind  the  wall 
together  into  a  solid  whole;  and  (3)  to  fill  the  spaces  and  voids  in 
the  masonry  and  keep  out  the  water.     Also,  a  good  mortar  should 
be  soft  and  plastic  so  that  it  will  work  properly  besides  being 
capable  of  hardening  and  becoming  strong,  dense,  and  impervious. 

In  general,  the  kind  of  mortar  used  depends  upon  the  kind  of 
masonry  and  the  loads  the  masonry  is  to  bear. 

Lime  mortar  is  usually  used  with  rubble  masonry,  often  with 
squared  stone  masonry,  and  rarely  with  cut  stone  or  ashlar 
masonry.  Probably  more  lime  mortar  is  used  than  any  other 
kind  as  it  is  very  suitable  for  masonry  where  the  loads  are  small. 
This  mortar  is  composed  of  1  part  of  lime  paste  to  2^2  to  3  parts 
of  good,  clean,  fine,  sharp  sand.  See  chapter  on  "  Limes  and 
Lime  Mortars"  for  a  further  discussion  of  this  mortar. 

A  Portland  cement  mortar  is  usually  used  with  cut  stone  or 
ashlar  masonry,  sometimes  with  squared  stone  masonry,  and 
rarely  with  rubble  masonry.  This  mortar  should  always  be  used 
where  the  unit  load  on  the  masonry  is  large.  The  proportions 
usually  vary  from  1  part  of  portland  cement  to  from  1  to  4  parts 
of  sand  according  to  the  strength  desired.  See  chapter  on 
" Portland  Cement  and  Cement  Mortars"  for  a  further  discussion 
of  this  mortar. 

A  mortar  made  of  Portland  cement,  lime,  and  sand  may  be 
used  with  any  of  the  three  classes  of  stone  masonry  as  conditions 
permit.  This  mortar  is  stronger  than  lime  mortar,  and  weaker, 
more  plastic,  and  more  impervious  than  an  ordinary  portland 
cement  mortar. 

157.  Dressing  of  Stone  Masonry. — Dressing  is  the  cutting 
of  the  side  and  bed  joints  of  the  stone  to  plane  surfaces,  usually 
at  right  angles  to  each  other.     Care  should  be  taken  to  make  the 
bed  a  plane  surface  so  that  the  pressure  will  be  distributed  evenly 
over  all  of  the  stone  and  also  so  that  the  bending  stresses  in  the 
stone  will  be  a  minimum.     Great  smoothness  is  not  desirable 
in  the  joints  as  slightly  rough  surfaces  offer  a  greater  resistance 
to  slipping  and  also  tend  to  increase  the  adhesion  of  the  mortar. 

158.  Bond  in  Stone  Masonry. — Bond  in  masonry  is  the  over- 
lapping of  the  stone  so  as  to  tie  the  wall  together  both  longitudi- 


STONE  AND  BRICK  MASONRY 


123 


nally  and  transversely,  and  is  of  great  importance  to  the  strength 
of  the  wall.  The  stone  in  any  course  should  be  laid  so  that  they 
will  overlap  or  break  joints  with  those  in  the  course  below,  and 
in  such  a  manner  that  each  stone  will  be  supported  by  two  (or 
three)  below  and  will  aid  in  supporting  at  least  two  above  it  in 
the  wall. 

A  very  strong  bond  is  made  by  laying  some  of  the  stone  with 
their  greatest  dimension  perpendicular  to  the  face  of  the  wall. 
Such  stone  are  called  "  headers."  In  thin  walls  the  headers 
should  be  long  enough  to  extend  clear  through  the  wall. 

Stone  laid  with  their  greatest  dimension  parallel  with  the  face 
of  the  wall  are  called  "stretchers." 

159.  Backing  in  Stone  Masonry. — Ashlar  or  cut-stone  masonry 
is  usually  backed  with  coursed  rubble  masonry  and  sometimes 


FIG.  68. — Methods  of  finishing  horizontal  joints. 

with  brick  masonry.  Squared-stone  masonry  is  sometimes 
backed  with  rubble  or  brick  masonry. 

Great  care  should  be  taken  to  secure  a  good  bond  between  the 
facing  masonry  and  the  backing.  Headers  should  be  frequently 
used.  For  the  best  bond,  the  backing  should  be  built  up  with 
the  facing  masonry. 

160.  Pointing  of  Stone  Masonry. — Pointing  is  the  refilling  of 
the  edges  of  the  joints  in  the  masonry  as  compactly  as  possible 
and  to  a  depth  of  about  1  in.  with  mortar  especially  prepared  for 
that  purpose.  Only  a  very  good  cement  mortar  such  as  a  1:1 
or  a  1 : 2  portland  cement  mortar  should  be  used.  Sometimes  a 
good  lime  mortar  is  used  for  some  classes  of  masonry. 

The  four  general  ways  of  pointing  the  edges  of  the  horizontal 
joints  in  cut  stone  masonry  are  flush  joints,  weather  joints, 
grooved  joints,  and  bead  joints.  The  vertical  joints  are  pointed 
in  the  same  manner  as  the  horizontal  ones,  except  that  in  weather 
joints,  the  vertical  joints  are  made  flush.  Care  should  be  taken 
not  to  reverse  the  slope  in  the  weather  joint  as  this  would  allow 
water  to  collect  in  the  joint  and  tend  to  weaken  the  masonry. 


124  MATERIALS  OF  CONSTRUCTION 

161.  General  Rules  for  Laying  Stone  Masonry. — The  following 
general  rules  for  laying  stone  masonry  are  taken  from  '  Baker's 
Masonry  Construction."     These  principles  apply  to  all  classes  of 
stone  masonry. 

1.  The  largest  stone  should  be  used  in  the  foundation  to  give 
the  greatest  strength  and  lessen  the  danger  of  unequal  settlement. 

2.  A  stone  should  be  laid  upon  its  broadest  face,  since  then 
there  is  better  opportunity  to  fill  the  spaces  between  the  stones. 

3.  For  the  sake  of  appearance,  the  larger  stone  should  be  placed 
in  the  lower  courses,  the  thickness  of  the    courses  decreasing 
gradually  toward  the  top  of  the  wall. 

4.  Stratified  stone  should  be  laid  upon  their  natural  bed, 
that  is,  with  the  strata  perpendicular  to  the  pressure,  since  they 
are  then  stronger  and  more  durable. 

5.  The  masonry  should  be  built  in  courses  perpendicular  to  the 
pressure  it  is  to  bear. 

6.  To  bind  the  wall  together  laterally  a  stone  in  any  course 
should  break  joints  with  or  overlap  the  stone  in  the  course  below; 
that  is,  the  joints  parallel  to  the  pressure  in  two  adjoining  courses 
should  not  be  too  nearly  in  the  same  line.     This  is  briefly  stated 
by  saying  that  the  wall  shall  have  sufficient  lateral  bond. 

7.  To  bind  the  wall  together  transversely  there  should  be  a 
considerable  number  of  headers  extending  from  the  front  to  the 
back  of  thin  walls  or  from  the   outside  to  the  interior  of  thick 
walls;  that  is,   the  wall  should  have  sufficient  transverse  bond. 

8.  The  surface  of  all  porous  stone  should  be  moistened   before 
being  bedded,  to  prevent  the  stone  from  absorbing  the  moisture 
from  the  mortar  and  thereby  causing  it  to  become  a  friable  mass. 

9.  The  spaces  between  the  back  ends  of  the  adjoining  stone 
should  be  as  small  as  possible,  and  these  spaces  and  the  joints 
between  the  stone  should  be  filled  with  mortar. 

10.  If  it  is  necessary  to  move  a  stone  after  it  has  been  placed 
upon  the  mortar  bed,  it  should  be  lifted  clear  and  reset,  as  at- 
tempting to  slide  it  tends  to  loosen  stones  already  laid  and  destroy 
the  adhesion,  and  thereby  injure  the  strength  of  the  wall. 

11.  An  unseasoned  stone  should  not  be  laid  in  the  wall  if  there 
is  any  likelihood  of  its  being  frozen  before  it  has  seasoned. 

162.  Waterproofing  Stone  Masonry. — As  most  of  the  stone 
used  for  masonry  is  practically  impermeable,  the  weak  or  permea- 
ble part  of  the  masonry  is  the  joints.     If  good  mortar  is  used  and 
all  of  the  spaces  between  the  stone  are  filled,  practically  no 


STONE  AND  BRICK  MASONRY  125 

water  will  pass  through.  Care  should  be  taken  to  see  that  all 
joints  are  carefully  pointed  and  that  all  cracks  are  filled  with  good 
mortar. 

Washing  or  painting  the  surface  of  the  masonry  exposed  to  the 
water  with  a  waterproofing  compound  (such  as  a  soap  and  alum 
solution,  hot  tar,  asphalt,  etc.)  will  aid  in  making  the  masonry 
water-tight. 

Sometimes  the  masonry  is  made  more  water-tight  by  incorpora- 
ting a  layer  of  felt  or  tar  paper,  painted  on  both  sides  with  tar  or 
asphalt,  in  the  wall.  Care  should  be  taken  to  make  the  ends  of 
the  felt  or  paper  overlap  so  that  no  cracks  or  holes  extend  through 
this  waterproofing  layer.  Such  a  waterproofing  layer  is  some- 
times applied  to  the  face  or  back  of  the  wall  instead  of  being  built 
in  the  wall. 

163.  Cleaning  Stone  Masonry. — When  the  masonry  is  com- 
pleted, the  surfaces  should  be  cleaned  to  remove  any  dirt,  mortar, 
etc.  adhering  to  the  wall.     The  cleaning  is  usually  done  by  brush- 
ing with  stiff  brushes  and  then  washing  with  water. 

Frequently,  the  stone  work  in  buildings  or  other  structures 
becomes  soiled  by  dirt  in  the  air,  or  smoke.  The  stone  work  may 
be  cleaned  with  soap  and  water  or  by  brushing  and  then  washing 
with  soap  and  water.  Sometimes  washing  with  a  dilute  acid 
solution  aids  in  cleaning  and  brightening  the  surface.  The  use 
of  the  sand  blast  is  very  effective  for  cleaning  purposes. 

164.  Strength  and  Other  Properties  of  Stone  Masonry.— The 
strength  of  stone  masonry  depends  not  only  upon  the  strength 
of  the  stone  in  compression  but  also  upon  the  accuracy  of  the 
dressing,  the  bond  between  the  stones,  and  the  thickness  and 
strength  of  the  mortar.     In  practically  all  of  the  observed  failures 
of  stone  masonry  under  compression,  the  mortar  failed  first  and 
squeezed  out,  thus  causing  bending  stresses  in  the  stone  which 
resulted   in   their  failure  by  tension  in  cross  bending.     About 
the  only  practical  way  of  determining  the  strength  of  good  stone 
masonry  is  to  note  the  loads  that  have  been  carried  by  it  without 
failure.     There    are    several    structures    of   first-class    masonry 
carrying  loads  of  approximately  400  Ib.  per  square  inch  without 
showing  any  signs  of  failure. 

Ashlar  or  cut  stone  masonry  is  the  best  of  all  stone  masonry  in 
quality,  and  it  is  used  in  all  important  structures  where  strength 
and  stability  are  required.  The  stone  used  should  not  be  longer 
than  3  to  5  times  their  depth,  nor  wider  than  2  to  3  times  the 


126  MATERIALS  OF  CONSTRUCTION 

depth,  depending  to  some  extent  upon  the  strength  of  the  stone. 

The  weight  per  cubic  foot  of  stone  masonry  may  be  taken  at 
about  5  Ib.  less  than  that  of  the  stone  used. 

The  modulus  of  elasticity  of  stone  masonry  in  compression  is 
about  2,000,000  Ib.  per  square  inch  for  rubble  masonry  and  about 
4,000,000  Ib.  per  square  inch  for  ashlar  masonry.  These  values 
are  approximate  only  and  depend  to  a  large  extent  upon  the  stone 
and  mortar  used  as  well  as  the  class  of  masonry  and  the  care 
with  which  it  is  constructed. 

The  amount  of  mortar  required  for  ashlar  masonry  is  about  2  or 
2%  cu.  ft.  per  cubic  yard  of  masonry;  for  squared  stone  masonry, 
from  3J^  to  5  cu.  ft.  per  cubic  yard  of  masonry;  and  for  rubble 
masonry,  from  7J^  to  10  cu.  ft.  per  cubic  yard  of  masonry. 

The  coefficient  of  expansion  of  stone  masonry  is  about 
0.0000035  per  degree  Fahrenheit. 

The  tensile  strength  of  masonry  is  very  small,  and,  therefore, 
stone  masonry  should  not  be  designed  to  carry  any  tension. 

As  stone  masonry  is  very  weak  in  tension,  it  is  also  weak  in 
cross  bending,  and  should  not  be  expected  to  carry  transverse  loads. 

165.  Safe  Loads  for  Stone  Masonry. — Safe  loads  for  stone 
masonry  in  tension  and  cross  bending  should  be  considered  as 
zero,  except  in  special  cases  where  there  are  special  designs  and 
constructions. 

The  working  stress  in  shear  should  be  taken  at  one-fourth  of 
the  safe  working  stress  in  compression.  See  tables  following  for 
safe  working  stress  in  compression. 

From  an  examination  of  the  loads  carried  by  different  classes 
of  the  best  stone  masonry  without  failure,  the  values  in  the 
following  table  may  be  assumed,  provided  that  each  kind  of 
stone  masonry  is  the  best  of  its  class : 

SAFE  LOADS  IN  COMPRESSION  FOR  THE  BEST  STONE  MASONRY 

GOOD  ORDINARY  PORTLAND  CEMENT 

MORTAR,  POUNDS  PER          MORTAR  1:2  Mix, 
KIND  OF  MASONRY  SQUARE  INCH  POUNDS  PER  SQUARE  INCH 

Rubble 140  to  200 

Squared  stone 200  to  280 

Limestone  ashlar 280  to  350                            600 

Sandstone  ashlar •        250  to  320                           500 

Granite  ashlar 350  to  400                           700 

The  building  laws  (1907)  of  the  city  of  Chicago  gave  the 
following  allowable  safe  loads  in  compression  for  masonry. 


STONE  AND  BRICK  MASONRY  127 

These  values  were  recommended  to  the  city  by  a  large  committee 
composed  of  the  leading  architects  and  engineers  of  Chicago. 

CITY  OF  CHICAGO 
ALLOWABLE  UNIT  STRESSES  FOR  MASONRY  IN  COMPRESSION 

All  values  are  in  pounds  per  square  inch 

PORTLAND 
CEMENT 
KIND  OF  MASONBY  LIME  MOBTAK       MOBTAB 

Rubble  masonry,  uncoursed 60  100 

Rubble  masonry,  coursed 120  200 

Ashlar  masonry,  coursed  limestone ...  400 

Ashlar  masonry,  coursed  sandstone ...  400 

Ashlar  masonry,  coursed  granite ...  600 

B.  BRICK  AND  HOLLOW  TILE  MASONRY 

166.  Brick  Masonry  in  General. — Brick  masonry  includes  all 
forms  of  masonry  composed  of  brick  and  mortar,  such  as  walls 
of  buildings,   backing  for  stone  and  concrete  masonry,  sewers, 
tunnels,  facing  for  stone  or  concrete  masonry,  arches,  etc.,  and 
sometimes  culverts,  piers,  abutments,  and  bridges. 

At  the  present  time,  brick  masonry  is  much  used  as  a  building 
material.  Good  brick  masonry  is  the  equal  of  stone  masonry 
in  strength,  durability,  and  appearance.  Some  of  the  advantages 
of  brick  masonry  are:  brick  resist  the  action  of  fire,  weather,  and 
the  acids  in  the  atmosphere ;  brick  can  be  secured  in  any  locality, 
and  of  most  any  size,  shape,  and  color;  brick  are  easy  to  lay  in  a 
wall;  brick  masonry  is  as  durable  as  stone  masonry ;  brick  masonry 
is  as  strong  as  stone  masonry,  with  the  exception  of  cut  stone 
masonry;  brick  masonry  is  often  cheaper  than  stone  masonry. 
Some  of  the  disadvantages  of  brick  masonry  are :  it  requires  skill 
to  lay  a  good  wall ;  poor  mortar  is  often  used  in  the  laying  of  the 
brick,  thus  making  a  wall  that  is  neither  strong  nor  durable. 

167.  Mortar  for  Brick  Masonry. — As  in  stone  masonry,  the 
mortar  in  brick  masonry  has  three  functions  to  perform :  namely, 
(1)  to  form  a  bed  or  cushion  to  take  up  any  inequalities  in  the 
brick  and  to  distribute  the  pressure  uniformly;  (2)  to  bind  the 
wall  into  a  solid  mass;  and  (3)  to  fill  the  spaces  and  voids  between 
the  brick  in  the  masonry  and  keep  out  the  water. 

In  general,  the  mortar  should  be  chosen  to  suit  the  character 
of  the  masonry  and  the  loads  that  it  is  to  bear.  For  strong  and 
impervious  masonry  or  masonry  which  may  be  under  water,  a 
Portland  cement  mortar  (of  a  mix  varying  from  a  1:2  to  1:4 


128  MATERIALS  OF  CONSTRUCTION 

according  to  conditions)  should  be  used.  For  small  loads  a  good 
lime  mortar  is  suitable,  while  for  medium  loads,  a  mortar  com- 
posed of  Portland  cement,  lime,  and  sand  may  be  used.  Clay 
or  loam  should  never  be  used  in  place  of  the  sand.  At  the  present 
time  most  of  the  brick  masonry  is  laid  in  lime  mortar  on  account 
of  its  cheapness. 

The  quantity  of  mortar  required  for  brick  masonry  depends 
upon  the  size,  of  the  brick  and  the  thickness  of  the  joints.  As 
many  of  the  building  brick  are  about  of  the  same  size,  most  of 
the  variation  in  the  quantity  of  mortar  needed  is  due  to  the 
thickness  of  the  joints. 

The  thickness  of  joints  in  brick  masonry  may  vary  from  ^  to 
Y±  in.,  depending  on  the  kind  of  brick  used  and  the  architectural 
effect  desired.  For  pressed  brick,  a  joint  of  about  ^{Q  in.  is 
desirable,  while  for  ordinary  brick  the  joint  should  be  from  %  to 
%in.  thick  for  good  work.  For  ordinary  backing  and  filling  and 
rough  work,  the  joints  are  usually  from  %  to  J^  in.  thick. 

168.  Laying  the  Brick. — The  following  principles  apply  to  all 
brick  laying: 

1.  All  brick  should  be  thoroughly  wet  before  laying,  so  that  they  will  not 
absorb  the  water  from  the  mortar.     While  this  wetting  is  important,  it  is 
often  neglected. 

2.  The  brick  should  be  laid  in  a  truly  horizontal  position  except  in  special 
cases. 

3.  The  top  edge  of  a  brick  should  be  laid  to  a  stretched  string. 

4.  The  masonry  should  be  built  in  courses  perpendicular  to  the  pressure 
it  is  to  bear. 

5.  Each  course  should  break  joints  with  the  courses  immediately  above 
and  below  it.     There  should  be  sufficient  longitudinal  bond. 

6.  Sufficient  transverse  bond  should  be  provided. 

7.  The  spaces  between  the  brick  should  be  completely  filled  with  mortar. 

8.  In  laying  the  brick,  a  layer  of  mortar  should  first  be  spread  over  the 
last  course  of  brick. 

9.  The  brick  should  be  firmly  pressed  in  place  in  this  mortar  with  a  slid- 
ing motion  which  will  force  the  mortar  to  fill  the  joint. 

10.  The  excess  mortar  squeezed  out  on  the  face  of  the  wall  should  be 
removed  with  the  trowel  and  applied  to  the  end  of  the  brick  so  as  to  aid  in 
filling  the  next  joint. 

169.  Improvements  in  Brick  Laying. — During  the  last  few 
years,  the  laying  of  brick  has  been  greatly  expedited  by  the  use 
of  three  innovations:  the  packet,  the  special  scaffold,  and  the 
fountain  trowel.     By  the  use  of  these  innovations,  together  with 
proper  instructions,  a  skilled  bricklayer  can  lay  three  or  four 
times  as  many  brick  as  he  could  before. 


STONE  AND  BRICK  MASONRY  129 

The  packet  is  a  small  wooden  frame  or  tray  upon  which  two 
rows  of  ten  brick  each  are  placed  on  edge  in  such  a  position  that 
the  mason  can  put  his  fingers  under  each  brick  while  it  is  upon  the 
packet.  The  brick  are  placed  on  the  packets  when  they  are 
unloaded  from  the  wagon  or  car,  and  are  transported  on  the 
packets  to  the  scaffold.  The  brick  may  be  sorted  as  they  are 
placed  on  the  packets. 

The  special  scaffold  is  simply  a  shelf  or  bench  about  two  and  a 
half  feet  above  the  platform  on  which  the  mason  stands.  The 
packets  are  placed  on  this  scaffold.  Hence,  the  mason  does  not 
have  to  stoop  over  and  pick  up  each  brick  from  the  floor  of  the 
platform  on  which  he  stands,  thus  saving  time  and  energy. 

The  fountain  trowel  is  a  metal  can  shaped  something  like  a 
low  shoe.  The  heel  is  used  to  scoop  up  the  mortar  from  the  box, 
and  the  mortar  is  poured  upon  the  brick  through  a  narrow  open- 
ing in  the  toe  about  4  in.  long.  This  fountain  trowel  makes  it 
possible  to  spread  a  much  greater  quantity  of  mortar  in  a  given 
time,  and  also  permits  the  use  of  a  softer  mortar  which  fills  the 
joints  better. 

170.  Bond  in  Brick  Masonry. — The  bond  is  the  arrangement 
of  the  brick  in  courses  in  such  a  way  as  to  tie  the  wall  together 
both  longitudinally  and  transversely.  The  brick  in  one  course 
should  always  break  joints  with  those  in  the  course  below. 

A  stretcher  is  a  brick  laid  with  its  greatest  dimension  parallel 
to  the  face  of  the  wall,  while  a  header  is  a  brick  laid  with  its 
greatest  dimension  perpendicular  to  the  face  of  the  wall.  A 
course  is  a  layer  of  brick,  and  is  usually  horizontal. 

The  three  principal  ways  of  bonding  are  the  common,  English, 
and  Flemish  methods.  In  the  common  bond,  from  four  to  seven 
courses  of  stretchers  are  laid  to  one  course  of  headers.  The 
English  bond  consists  of  alternate  courses  of  headers  and 
stretchers.  In  the  Flemish  bond,  the  headers  and  stretchers 
alternate  in  each  course,  and  the  brick  are  so  placed  that  the 
outer  end  of  a  header  lies  in  the  middle  of  a  stretcher  in  the  course 
below. 

Brick  veneer  consists  of  a  single  layer  of  brick  placed  on  the 
face  of  the  wall.  Great  care  must  be  taken  in  the  bonding  of  this 
veneer  to  the  rest  of  the  wall  if  these  brick  are  to  carry  any  of  the 
load.  One  of  the  ways  of  bonding  is  a  secret  bond  as  shown  in 
the  sketch.  Another  way  is  to  use  metal  ties  extending  from 
the  joints  in  the  veneer  to  the  joints  in  the  filling. 

9 


130  MATERIALS  OF  CONSTRUCTION 

In  hollow  walls,  the  bonding  of  the  outer  layers  to  the  inner 
layers  is  usually  accomplished  by  long  metal  ties. 

Arches  in  brick  work  are  usually  built  with  a  series  of  header 
courses  in  which  the  brick  are  laid  on  edge.  Such  arches  are 
called  row-lock  arches.  Another  method  is  to  lay  the  brick 
with  continuous  radial  joints  with  the  brick  laid  partly  as  headers 
and  partly  as  stretchers.  Specially  prepared  brick  must  be 
used  for  this  method. 

171.  Pointing  of  Brick  Masonry. — After  the  wall  is  built,  the 
edges  of  the  exposed  joints  are  pointed  by  refilling  them  to  a 
depth  of  about  one  inch  with  specially  prepared  mortar.  This 


1         1 

I     1     1     1     1 

1 

1         1 

1          1          1 

1         1 

1         1         1 

1          1 

1     1     1     1     1 

1 

1         1 

I     I     I     I     I  . 

i '  i   i ,  i   i  :r    . '   i ,   1 1  E 


ii    ii    i         .  i    i 


i    i 


ii    ii   r~       i L j L_ 

i       i     ^^     i       i    i       i 

FIG.  69. — Common    bond       FIG.  70. — English  bond  FIG.  71.. — Flemish 

of    brickwork.  of  brickwork.  bond   of  brickwork 

mortar  is  usually  richer  than  that  used  in  building  the  wall. 
Sometimes  the  pointing  mortar  is  colored  so  as  to  secure  pleasing 
effects. 

The  four  general  ways  of  refilling  the  horizontal  joints  are  by 
making  what  are  known  as  flush,  bead,  groove,  and  weather  joints. 
The  vertical  joints  are  pointed  in  the  same  way  except  that  when 
the  horizontal  joints  are  weather  joints,  the  vertical  ones  are  made 
flush.  There  are  several  other  varieties  of  pointing  which  are 
not  known  by  any  general  names.  When  the  slope  of  the  weather 
joint  is  reversed  (sometimes  called  a  struck  joint),  it  allows 
water  to  collect  in  the  joint  and  penetrate  into  the  masonry. 

172.  Waterproofing  Brick  Masonry. — Brick  masonry  may  be 
made  water-tight  by  constructing  it  of  impervious  brick  and 
mortar. 

Another  way  is  to  incorporate  a  layer  of  tarred  paper  or  felt 
(painted  with  asphalt  or  tar)  in  the  wall. 

If  the  wall  is  already  built,  it  can  be  made  more  water-tight 
by  painting  it  with  a  soap  and  alum  solution,  a  tar  or  asphalt 
preparation,  or  some  other  waterproofing  compound.  Sometimes 
it  is  given  a  coating  of  impervious  mortar  or  of  an  impervious 
bituminous  mastic. 


STONE  AND  BRICK  MASONRY  131 

The  methods  of  rendering  a  stone  wall  water-tight  may  be 
used  to  make  a  brick  wall  waterproof. 

173.  Cleaning  Brick  Masonry. — Brick  masonry  may  be  cleaned 
by  the  same  methods  as  are  used  for  cleaning  stone  masonry 
(see  the  article  on  " Cleaning  Stone  Masonry"). 

Mortar  sometimes  sticks  so  tightly  to  the  brick  that  a  metal 
tool  is  required  to  remove  it. 

Enameled  brick  can  be  cleaned  with  caustic  soda  or  sodium 
carbonate,  which  does  not  have  any  effect  on  the  brick  or 
cement  and  lime  mortar. 

174.  Strength  and  Other  Properties  of  Brick  Masonry. — The 
weight  of  the  best  pressed  brick  masonry  with  thin  joints  is 
about   145  Ib.  per  cubic  foot;  of  brick  masonry  of    ordinary 
quality,  125  Ib.  per  cubic  foot;  and  of  soft  brick  masonry  with 
thick  j  oints,  100  Ib.  per  cubic  foot.     These  values  are  approximate. 

The  strength  of  brick  masonry  depends  more  upon  the  strength 
of  the  mortar,  the  bond,  and  the  workmanship  than  upon  the 
strength  of  the  brick.  When  it  is  desired  to  have  strong  masonry, 
a  portland  cement  mortar  must  be  used. 

Occasionally,  the  transverse  strength  of  the  brick  masonry  is 
of  importance,  as  in  some  cases  the  masonry  acts  as  a  beam  (fre- 
quently when  door  openings  are  cut  in  a  brick  wall  after  it  is 
built).  A  few  tests  have  given  results  varying  from  50  Ib.  per 
square  inch  to  300  Ib.  per  square  inch  in  cross  bending,  according 
to  the  quality  of  the  brick  and  the  mortar. 

The  modulus  of  elasticity  of  good  brick  masonry  in  compression 
is  about  2,000,000  Ib.  per  square  inch. 

The  coefficient  of  expansion  is  approximately  0.0000030  per 
degree  Fahrenheit  for  pressed  brick  masonry. 

The  shearing  strength  of  brick  masonry  probably  varies  from 
10  to  25  per  cent  of  the  shearing  strength  of  the  brick,  depending 
upon  the  quality  of  the  mortar  used. 

The  compressive  strength  of  brick  masonry  is  of  the  most 
importance.  A  number  of  tests  have  been  made  on  the  crushing 
strength  of  brick  masonry  piers.  The  first  sign  of  failure  was 
usually  a  popping  or  cracking  sound  followed  a  little  later  by 
the  appearance  of  cracks  which  gradually  increased  in  size 
until  the  failure  was  complete.  In  nearly  all  of  the  tests,  the 
mortar  failed  before  the  brick. 

The  following  table  gives  results  of  compression  tests  made 
upon  some  brick  piers  at  the  Watertown  (U.  S.)  Arsenal: 


132 


MATERIALS  OF  CONSTRUCTION 
CRUSHING  STRENGTH  OF  BRICK  PIERS 


Watertown  Arsenal  tests 
of  1904 

Age  6  months 

Compressive  strength, 

Per  cent  of  average  crushing 

pounds  per  square  inch 

strength  of  the  brick 

Kind  of  brick 

Neat 
Portland 
cement 

1  Portland 
3  sand 

1  lime 
3  sand 

Neat 
Portland 
cement 

1  Portland 
cement 
3  sand 

1  lime 
3  sand 

Face  brick 

Dry  pressed  face  brick  

2,880* 

2,400 

1,517 

26 

21 

13 

Repressed  mud  brick  

1,925 

1,670 

1,260 

28 

25 

19 

Common  brick 

Wire  cut  stiff  mud  brick.  . 

4,021 

2,410* 

1,420 

31 

19 

11 

Hard  sand  struck  brick  .  .  . 

4,700* 

1,800* 

994 

42 

16 

9 

Hard  sand  struck  brick  .  .  . 

1,969 

1,800 

733 

44 

40 

16 

Hard  sand  struck  brick  .  .  . 

1,400 

1,411 

718 

24 

24 

12 

Light    hard    sand    struck 

brick  

1,510* 

1,519 

732 

23 

23 

11 

Light    hard    sand    struck 

1,061 

1,224 

465* 

20 

23 

9 

*Age  1  month. 

175.  Allowable  Working  Loads  for  Brick  Masonry. — Safe 
working  loads  for  brick  masonry  in  tension  and  cross  bending 
should  be  considered  as  zero,  except  in  special  cases  where  there 
are  special  designs  and  constructions. 

In  the  case  of  a  lintel,  the  actual  load  on  it  is  very  uncertain. 
This  load  may  be  assumed  to  be  the  weight  of  all  the  masonry 
vertically  above  the  lintel,  including  such  loads  as  may  be  trans- 
mitted to  the  masonry  from  floors,  etc.  Another  assumption 
is  to  take  the  load  as  the  weight  of  the  triangle  of  masonry  above 
the  lintel,  considering  the  span  of  the  lintel  as  the  base  of  the 
triangle  and  assuming  that  the  sides  of  the  triangle  make  an 
angle  of  45  degrees  with  the  base.  This  latter  assumption  may 
be  a  little  unsafe,  but  if  the  angle  of  the  sides  is  changed  to  60 
degrees,  the  assumption  gives  results  that  are  safe  for  most  cases. 
If  there  is  any  doubt  in  regard  to  the  safety  of  the  lintel,  it  is 
better  to  construct  an  arch  over  the  opening. 

The  allowable  working  stress  in  shear  for  brick  masonry  may 
be  taken  at  one-fourth  of  the  allowable  working  stress  in 
compression. 

The  following  table  gives  the  safe  working  stresses  in  com- 
pression for  brick  masonry  as  recommended  by  a  committee  of 


STONE  AND  BRICK  MASONRY 


133 


Chicago  Engineers  and  Architects  in  1908  for  the  building  laws 
of  that  city.     This  table  represents  good  practice. 

SAFE  WORKING  LOADS  IN  COMPRESSION  FOR  BRICK  MASONRY 


Safe 

load  in 

Kind  of  brick 

Kind 
of 

pounds 

mortar 

per 

square 

inch 

Paving  brick  

1:3 

Portland  cement  and  sand.  . 

350 

Pressed  and  sewer  brick,  strength  5,000  Ib  .  .  . 

1:3 

Portland  cement  and  sand.  . 

250 

Select  hard  common  brick,  strength  2,500  Ib  . 

1:3 

Portland  cement  and  sand  .  . 

200 

Select  hard  common  brick,  strength  2,500  Ib  . 

1 

Portland  cement,   1  lime,  3 

sand 

175 

inch  .•  

1:3 

Portland  cement  and  sand.  . 

175 

Common  brick,  strength  1,800  Ib.  per  square 

inch 

1:3 

Natural  cement  and  sand 

150 

Common  brick,  strength  1,800  Ib.  per  square 

inch  

1 

Portland  cement,  1  lime,  3 

sand 

125 

1:3 

Lime  and  sand 

100 

176.  Efflorescence. — Efflorescence    is    a    white    deposit    that 
frequently  forms  on  the  surface  of  brick  masonry,  especially  in 
moist  climates  and  in  damp  places,  and  spoils  the  appearance 
of  the  brickwork.     The  mortar  in  the  masonry  absorbs  water 
and   this   water  dissolves   some   of   the  salts  of  potash,  soda, 
magnesia,  etc.  that  are  in  the  lime  or  cement.     Then,  when  the 
water  is  evaporated  from  the  surface  of  the  brickwork,  it  leaves 
these  salts  in  the  form  of  a  white  deposit.     Generally,  there  is  a 
greater   deposit   from   a   lime   mortar   than   from  a  natural  or 
Portland  cement  mortar.     A  portland  cement  mortar  has  the 
least  amount  of  deposit.     Sometimes  the  efflorescence  originates 
in  the  brick,  particularly  if  the  brick  were  burned  with  sulphurous 
coal,  or  were  made  from  clay  containing  iron  pyrites. 

Efflorescence  can  often  be  prevented  by  making  the  wall  as 
water-tight  as  possible  and  by  keeping  water  from  leaking  into  the 
wall.  Painting  the  wall  with  a  soap  and  alum  solution  tends  to 
prevent  efflorescence. 

Efflorescence  can  be  removed  from  the  wall  by  the  use  of 
scrubbing  brushes  and  soap  and  water  or  a  dilute  solution  of 
hydrochloric  acid  in  water. 

177.  Hollow  Tile  Masonry. — Hollow  tile  masonry  is  composed 
of  hollow  terra  cotta  or  tile  building  blocks  laid  in  a  portland 


134 


MATERIALS  OF  CONSTRUCTION 


cement  mortar.  This  masonry  is  light  in  weight  and  fireproof. 
It  is  used  for  backing  of  walls,  for  entire  walls,  and  for  partitions 
and  floors. 

In  walls,  the  blocks  are  usually  laid  with  their  openings  vertical 
instead  of  horizontal.     When  the  openings  are  vertical,  wire 


Metal  Ties.  Header  Courses.  Flemish  Bond. 

FIG.  72. — Hollow  tile  masonry  wall  veneered  with  brick. 

screen  is  often  laid  in  the  horizontal  joints  to  aid  in  holding  the 
mortar  in  place.  The  mortar  should  be  a  1:2  portland  cement 
mortar,  preferably  containing  a  small  amount  of  lime  paste  not 
to  exceed  ten  per  cent.  Good  hollow  tile  masonry  can  be  safely 
used  for  the  load-carrying  walls  of  ordinary  buildings  and  dwell- 
ings that  are  three  stories  or  less  in  height. 

Fireproof  floors  are  often  constructed  of  special  hollow  terra 
cotta  blocks  in  buildings  of  steel  or  reinforced  concrete  construc- 
tion. These  blocks  are  set  in  portland  cement  mortar  and  are 
used  as  flat  arches  between  the  I-beam  or  reinforced  concrete 
beam  joists.  A  layer  of  concrete,  about  two  inches  thick,  is 
usually  placed  on  top  of  the  blocks  to  form  a  wearing  surface  for 
the  floor. 


CHAPTER  IX 

TIMBER 

A.  TREES 

178.  Timber  Trees  in  General. — Wood  has  long  been  used  as  a 
structural  material  because  it  could  be  obtained  in  most  every 
locality  and  was  easily  adapted  for  use.    While  there  are  hundreds 
of  varieties  of  trees,  yet  only  a  few  species  (probably  less  than 
25  distinct  species)  are  of  great  commercial  importance. 

Practically  all  of  the  woods  used  for  structural  materials  are 
produced  by  the  seed-bearing  trees.  These  trees  are  divided 
into  three  groups :  namely,  the  conifers,  or  soft  woods  (pine,  spruce, 
fir,  cedar,  etc.);  the  broad-leaved  trees,  or  hard  woods  (oak, 
maple,  ash,  walnut,  hickory,  etc.);  and  the  tropical  trees  (bam- 
boos, rattans,  palms,  etc.). 

Of  these  three  groups,  the  conifers,  which  are  found  throughout 
the  northern  hemisphere,  are  the  most  important  structurally. 
The  broad-leaved  trees  are  found  practically  all  over  the  world, 
and  they  are  next  to  the  conifers  in  structural  importance.  Of 
the  soft-  and  hard-wood  trees,  probably  the  pine,  fir,  hemlock, 
spruce,  cedar,  oak,  hickory,  ash,  poplar,  maple,  cypress,  and 
walnut  are  the  most  important.  Possibly  the  bamboo  may  also 
be  classed  as  an  important  structural  timber,  especially  in  the 
tropical  countries. 

There  is  no  sharp  distinction  in  hardness  between  the  soft 
woods  and  the  hard  woods,  as  some  of  the  hard  woods  (such  as 
poplar  and  bass  wood)  are  softer  than  some  of  the  pines. 

According  to  the  manner  of  their  growth,  trees  may  be  divided 
into  two  classes — the  exogenous  or  outward  growing  trees  (coni- 
fers and  broad-leaved  trees) ,  and  the  endogenous  or  inner  growing 
trees. 

179.  Structure   of  Exogenous  Trees. — The   structure   of  an 
exogenous  tree  consists  of  three  parts — the  bark,  the  sapwood, 
and  the  heartwood.     The  bark  is  a  protective  tissue  found  on 
the  outside  of  the  tree  trunk  and  varying  from  one  quarter  to 
two  inches  in  thickness.     It  is  valueless  as  a  structural  material 
and  is  always  removed  soon  after  the  tree  is  felled  because  it 

135 


136  MATERIALS  OF  CONSTRUCTION 

tends  to  hasten  the  decay  of  the  wood.  The  sap  wood  is  just 
inside  of  the  bark  and  is  made  up  of  the  soft  thin-walled  cells 
which  form  the  living  part  of  the  tree.  The  heartwood,  which 
is  circular  in  shape  and  darker  in  color  than  the  sapwood,  is 
inside  of  the  sapwood.  The  heartwood  consists  of  many  fibrous 
bundles  which  give  the  wood  its  strength  and  stiffness. 

The  wood  of  the  exogenous  trees  is  made  up  of  bundles  of  long 
cells  and  fibers  whose  long  axes  are  usually  parallel  to  the  tree 


Bar* 

Heart  Wood 
Sap  Woo* 
Spring  lTood(Ly/)V 


FIG.  73.  —  Cross-section  of  a  tree  showing  annual  rings. 

trunk.  These  vertical  bundles  are  crossed  in  a  radial  direction 
by  plates  of  tissue  or  radial  cells  extending  from  the  pith  at  the 
center  of  the  tree  to  the  soft  tissue  (sapwood)  on  the  outside. 
These  radial  cells  are  called  medullary  rays  and  help  to  bind  the 
longitudinal  fibers  more  firmly  together  besides  forming  com- 
munications between  the  center  of  the  tree  and  the  outside. 
There  are  resin  ducts  scattered  through  the  wood  of  the  conifers 
and  hollow  ducts  or  vessels  in  the  wood  of  the  broad-leaved  trees. 

The  conifers  are  more  uniform  in  structure  than  are  the  broad- 
leaved  trees,  whose  structure  is  often  very  complex. 

180.  Growth  of  Exogenous  Trees.  —  The  exogenous  trees  (coni- 
fers and  broad-leaved  trees)  increase  in  size  by  the  annual 
formation  of  new  wood  on  the  outer  surface.  The  conifers  can 
be  recognized  by  their  needle  leaves,  resinous  bark,  and  cones, 
while  the  broad-leaved  trees  can  be  distinguished  by  their  broad 
flaring  leaves. 

An  exogenous  tree  grows  in  diameter  when  new  and  branching 
bundles  of  hollow  fibers  appear  under  the  bark  and  form  an 
annular  ring  on  the  outer  edge  of  the  sapwood.  This  happens 
once  during  each  growing  season,  which  extends  through  the 
spring  and  summer.  The  growth  is  more  rapid  in  the  spring 
than  in  the  summer  and  this  variation  in  growth  causes  a  differ- 
ent appearance  in  the  wood  fibers,  the  summer  wood  usually 
being  darker  in  color  and  denser  than  the  spring  wood.  This 


TIMBER  137 

makes  the  cross-section  of  the  tree  look  like  a  number  of  con- 
centric circular  rings,  each  ring  representing  a  year's  growth. 
The  age  of  a  tree  can  be  determined  by  counting  the  number  of 
annular  rings.  The  thickness  of  an  annular  ring  varies  from 
0.01  to  0.5  in.,  with  an  average  of  about  0.10  to  0.15  in.  The 
last  few  rings  form  the  sapwood  which  is  light  in  color  and  usually 
from  H  to  4  in.  thick.  The  rings  inside  the  sapwood  form  the 
heartwood  which  contains  from  25  to  85  per  cent  of  the  wood 
of  the  tree,  according  to  the  kind  of  tree  and  the  conditions  of 
growth.  The  time  required  for  the  sapwood  to  change  to 
heartwood  varies  from  a  few  years  in  the  fir  to  many  years  in  the 
oak. 

The  exogenous  trees  grow  in  length  because  each  annular 
layer  extends  over  the  others,  thus  increasing  the  length.  Be- 
cause of  the  conical  shape  of  the  tip,  the  increase  in  length  may 
be  much  greater  than  the  increase  in  diameter. 

Knots  in  a  tree  are  caused  by  the  encasement  of  a  limb  by  the 
successive  annual  layers  of  wood.  When  a  board  is  sawed-  out 
of  a  tree,  the  knot  is  the  portion  of  the  branch  contained  in  the 
board,  and  the  fibers  of  the  knot  are  usually  about  perpendicular 
to  the  other  fibers  in  the  board.  A  loose  knot  is  one  that  is. 
loose  or  badly  cracked  or  checked  so  as  not  to  be  solid  in  the 
board,  and  it  is  usually  composed  of  dead  wood.  A  sound  knot 
is  one  that  is  solid  and  contains  no  appreciable  cracks  or  checks. 
It  is  usually  composed  of  living  wood. 

181.  Structure  and  Growth  of  Endogenous  Trees. — These 
trees  are  largely  confined  to  the  tropical  regions,  and  the  palms 
and  bamboo  are  about  the  only  ones  of  structural  importance. 

The  wood  elements  of  endogenous  trees  are  similar  to  those  of 
exogenous  trees  but  their  arrangement  is  different.  The  fibrous 
bundles  do  not  form  concentric  circles  around  the  center  of  the 
tree,  but  are  scattered  throughout  the  wood  where  they  curve 
inward  and  outward  among  each  other  thus  making  a  more 
complex  structure. 

Endogenous  trees  increase  in  diameter  and  length  by  the 
intermingling  of  new  wood  fibers  with  the  old.  The  growth  of 
the  fibers  is  apt  to  be  more  rapid  in  the  outer  part  of  the  stem, 
thus  causing  the  outer  part  to  be  more  dense  and  solid  than  the 
inner.  When  the  growth  is  very  rapid,  a  hollow  is  formed  in  the 
center  of  the  stem,  because  of  the  insufficient  growth  and 
the  rupture  of  the  inner  fibers.  Knots  or  joints  are  often  found 


138 


MATERIALS  OF  CONSTRUCTION 


at  the  places  where  leaves  have  issued.     The  bamboos  have 
hollow  centers,  while  the  palms  and  yuccas  have  pithy  centers. 

182.  Grain  and  Texture  of  Wood. — Depending  on  the  charac- 
ter and  arrangement  of  wood  elements,  the  width  of  growth 


(a)  Straight  grain. 


(&)   Cross  grain. 


(c)  Twisted  grain. 
FIG.  74. — Showing  the  grain  of  wood. 

rings,  etc.,  wood  may  be  described  as  fine  or  coarse  grained, 
straight  or  twisted  or  cross  grained,  curly,  "  bird's-eye,"  or 
mottled  grained,  etc. 

Woods  are  fine  grained  if  their  growth  rings  are  narrow,  and 
coarse  grained  if  their  growth  rings  are  wide.  Woods  may  be 
said  to  be  rough  or  smooth  grained  according  to  the  appearance 
of  the  surface.  They  are  straight  grained  if  the  fibers  are  straight 
and  parallel  to  the  axis  of  the  tree;  twisted  if  the  fibers  follow  a 
spiral  course  around  the  tree;  cross  grained  if  the  fibers  change 
direction  during  the  growth;  curly  grained  if  the  fibers  tend  to 
form  short  curves  or  curls  (as  in  curly  birch);  mottled  if  the 
appearance  has  a  mottled  effect.  " Bird's-eye"  is  probably  due 
to  the  layer  of  wood  next  to  the  bark  becoming  pitted  or 
marked  by  small  projections,  probably  caused  by  the  presence  of 
undeveloped  buds  as  in  " bird's-eye"  maple. 

Woods  may  be  said  to  have  coarse  or  fine  texture  if  the  ele- 
ments are  large  or  small.  The  texture  is  even  if  the  fibers  are  all 
of  about  the  same  size,  and  uneven  if  the  size  varies. 

183.  Color  and  Odor  of  Wood. — Color  helps  in  identifying 
the  species  of  wood.  Most  new  wood  is  almost  colorless  but 
becomes  yellowed  after  a  few  years  and  usually  deepens  in  color 
when  the  sapwood  changes  to  heartwood.  The  color  may  be 
variable  or  uniform  throughout  the  heartwood  and  may  be 


TIMBER  139 

lighter  or  darker  according  to  the  species  and  the  manner  of 
growth.  Deep  color  is  nearly  always  due  to  the  infiltration  of 
resins,  pigments,  tannins,  etc.  into  the  heartwood.  jUl  woods 
darken  more  or  less  when  exposed  for  a  time  to  air  or  immersed 
in  water.  Hence,  the  natural  color  can  only  be  observed  in 
newly  cut  wood.  Color  aids  in  distinguishing  the  heartwood 
from  the  sapwood,  as  the  heartwood  is  nearly  always  darker 
than  the  sapwood. 

All  woods  possess  a  characteristic  odor,  though  in  some  cases  it 
is  not  readily  distinguished.  The  odor  is  due  to  foreign  chemical 
compounds  in  the  wood  and  is  usually  more  pronounced  in 
heartwood  than  in  sapwood.  The  odors  of  green  wood,  seasoned 
timbers,  and  decaying  wood  are  different  in  different  species  and 
aid  in  identifying  the  different  species.  A  few  of  the  woods  lose 
most  of  their  odor  when  they  are  seasoned. 

184.  General  Characteristics  of  Conifers — Pine,  Fir,  Spruce.— 
White  Pine. — Light,  soft,  straight  grained,  easily  worked,  but 
not  very  strong.  Light  yellowish  brown  color  often  tinged 
slightly  with  red.  Used  for  pattern  making  and  interior  finishing. 

Red  Pine  (Norway  Pine). — Light,  hard,  coarse  grained,  com- 
pact, with  few  resin  pockets.  Light-red  color  with  a  yellow  or 
white  sapwood.  Used  for  all  purposes  of  construction. 

Yellow  Pine  (Long  Leaf). — Heavy,  hard,  strong,  tough,  coarse 
grained,  and  very  durable  when  dry  and  well  ventilated.  Cells 
are  dark  colored  and  very  resinous.  Color,  light  yellowish-red 
or  orange.  Cannot  be  used  in  contact  with  the  ground,  as  it 
then  decays  rapidly.  Used  for  heavy  framing  timbers  and 
floors. 

Yellow  Pine  (Short  Leaf). — Varies  greatly  in  the  amount  of 
sap  and  quality.  Cells  are  broad  and  resinous  with  numerous 
large  resin  ducts.  Medullary  rays  well  marked.  Color,  orange 
with  white  sapwood.  Used  as  a  substitute  for  long  leaf  pine. 

Douglas  Fir  (Oregon  Fir). — Hard  and  strong  but  varying 
greatly  with  age,  conditions  of  growth,  and  amount  of  sap. 
Durable  but  difficult  to  work.  There  are  two  varieties,  red  and 
yellow,  of  which  the  red  is  the  more  valuable.  Color,  light  red  to 
yellow  with  a  white  sapwood.  Used  in  all  kinds  of  construction. 

Black  Spruce. — Light,  soft,  close  grained,  straight  grained,  and 
satiny.  Color,  light  red  and  often  nearly  white.  Resists  decay 
and  the  destructive  action  of  Crustacea.  Used  for  piles,  framing 
timbers,  submerged  cribs,  and  cofferdams. 


140  MATERIALS  OF  CONSTRUCTION 

White  Spruce. — Similar  to  black  spruce,  but  it  is  not  so  com- 
mon. Light-yellow  in  color  with  an  indistinct  sapwood.  Used 
for  lumber  in  construction  work. 

185.  General  Characteristics  of  Conifers — Other  Species. — 
Hemlock.— Soft,  light  brittle,  easily  splits.  Is  not  durable, 
is  likely  to  be  shaky,  and  has  a  coarse  uneven  grain.  Light 
brown  color  tinged  with  red,  and  often  nearly  white.  Resistant 
to  attacks  of  ants.  Used  for  cheap,  rough,  framing  timber  and 
some  finishing  lumber. 

White  Cedar. — Soft,  light,  fine  grained,  and  very  durable  in 
contact  with  the  soil.  Lacks  strength  and  toughness.  Light- 
brown  color  which  darkens  with  exposure.  Sapwood  is  very 
thin  and  nearly  white.  Used  for  water  tanks,  shingles,  posts, 
fencing,  cooperage,  and  boat  building. 

Red  Cedar. — Strong  pungent  odor,  repellant  to  insects.  Very 
durable  and  -compact,  brittle,  but  easily  worked.  Color,  dull- 
brown  tinged  with  red.  Used  for  posts,  sills,  ties,  fencing, 
shingles,  and  linings  for  chests,  trunks,  and  closets. 

Tamarack  (Larch). — Hard,  heavy,  strong,  durable.  Like 
spruce  in  structure  and  hard  pine  in  weight  and  appearance. 
Used  for  posts,  poles,  sills,  ties,  and  ship  timbers. 

Cypress. — Very  durable,  light,  hard,  close  grained,  brittle, 
easily  worked,  and  polishes  easily.  Color,  bright  clear  yellow 
with  a  nearly  white  sapwood.  Used  for  house  siding,  building 
lumber,  poles,  interior  finishing,  etc.  Resists  dampness  and 
excessive  heat. 

Redwood  (California  or  Giant) . — Light,  soft,  weak,  and  brittle. 
Grain  is  coarse,  even,  and  straight.  Easily  split  and  worked. 
Durable  when  in  contact  with  the  soil.  Shrinks  lengthwise  as 
well  as  crosswise.  Color,  bright  clear  red  becoming  darker  with 
exposure.  Used  for  ties,  posts,  poles,  and  as  a  general  building 
material. 

186.  General  Characteristic  of  Broad-leaved  Trees — Oak, 
Maple,  Ash,  Walnut. — White  Oak. — Heavy,  strong,  hard,  tough, 
and  close  grained.  Checks  if  not  carefully  seasoned.  Well- 
known  silver  grain.  Capable  of  taking  a  high  polish.  Color, 
brown  with  lighter  sapwood.  Used  for  framed  structures, 
shipbuilding,  interior  finish,  carriage,  and  furniture  making. 

Chestnut  Oak. — A  species  of  white  oak.  Very  durable  in 
contact  with  the  soil.  Dark-brown  color.  Used  for  ties. 


TIMBER  141 

Live  Oak. — Very  heavy,  hard,  tough,  and  strong.  Hard  to 
work.  Color,  light-brown  or  yellow  with  a  nearly  white  sap  wood. 
Used  in  shipbuilding  and  wagon  work. 

Red  and  Black  Oak. — More  porous  than  white  oak  and  softer 
and  less  strong.  Color,  darker  and  redder  than  white  oak. 
Used  for  furniture  and  interior  finish. 

Hard  Maple. — Heavy,  hard,  strong,  tough,  and  coarse  grained. 
Medullary  rays  are  small  but  distinct.  EaSy  t&  polish.  Color, 
very  light-brown  to  yellow.  Used  for  flooring,  interior  finish, 
and  furniture. 

White  Maple. — About  the  same  as  hard  maple  except  that  it  is 
lighter  in  weight  and  color.  Same  uses. 

White  Ash. — Heavy,  hard,  very  elastic,  coarse  grained,  and 
compact.  Tends  to  become  decayed  and  brittle  after  a  few  years. 
Reddish  brown  color  with  a  nearly  white  sapwood.  Used  for 
interior  finish  and  cabinet  work.  Unfit  for  structural  work. 

Red  Ash.— Heavy,  compact,  and  coarse  grained  but  brittle. 
Color,  rich-brown,  with  sapwood  a  light-brown  sometimes 
streaked  with  yellow.  Used  as  a  substitute  for  the  more 
valuable  white  ash. 

Green  Ash. — Heavy,  brittle,  hard,  and  coarse  grained.  Color, 
brown  with  lighter  sapwood.  Used  as  a  substitute  for  white  ash. 

White  Walnut  (Butternut). — Light,  soft,  coarse  grained,  com- 
pact, and  easily  worked.  Polishes  well.  Color,  light-brown 
turning  dark  on  exposure.  Used  for  interior  finish  and  cabinet 
work. 

Black  Walnut. — Hard,  heavy,  strong,  and  coarse  grained. 
Checks  if  not  carefully  seasoned.  Easily  worked.  Rich  dark- 
brown  color  with  a  light  sapwood.  Used  for  interior  finish 
and  furniture. 

187.  General  Characteristics  of  Broad -leaved  Trees — Other 
Species. — White  Elm. — Heavy,  hard,  strong,  tough,  and  very  close 
grained.  Difficult  to  split  and  shape.  Warps  badly  in  drying. 
Takes  a  high  polish.  Color,  light-clear-brown  often  tinged  with 
red  and  gray,  with  a  broad  whitish  sapwood.  Used  for  building 
cars,  wagons,  boats,  and  ships.  Used  for  sills,  bridge  timbers, 
ties,  furniture,  and  barrel  staves. 

Hickory. — Heaviest,  hardest,  toughest,  and  strongest  of  the 
American  woods.  Very  flexible.  Medullary  rays  numerous  and 
distinct.  Brown  in  color  with  a  valuble  white  thin  sapwood. 


142  MATERIALS  OF  CONSTRUCTION 

Used  for  carriages,  handles,  and  bent  wood  instruments.  Not 
used  for  structural  purposes  on  account  of  its  hardness  and 
liability  to  attack  by  boring  insects. 

Locust. — Heavy,  hard,  strong,  and  close  grained.  Very  durable 
in  contact  with  the  ground.  Hardness  increases  with  age.  Color, 
brown  (and  rarely  light-green)  with  yellow  sap  wood.  Used  for 
ties,  vehicles,  posts,  and  turned  ornaments. 

Gum. — Heavy,  hard,  tough,  and  close  grained.  Shrinks  and 
warps  badly  in  seasoning.  Not  durable  when  exposed  to  weather. 
Takes  a  high  polish.  Color,  bright-brown  tinged  with  red. 
Used  for  furniture,  hat  blocks,  wagon  hubs,  interior  finish. 

Mahogany. — Strong,  durable,  and  flexible  when  green,  and 
brittle  when  dry.  Free  from  shakes.  Not  very  liable  to  attacks 
of  dry  rot  and  worms.  Peculiarly  marked  by  short  straight 
lines  or  dashes.  Rapid  seasoning  causes  deep  shakes.  Color, 
red-brown  of  various  shades  and  often  varied  and  mottled. 
Used  for  interior  finish,  furniture,  veneers,  etc. 

Chestnut. — Light,  moderately  soft,  stiff,  and  of  coarse  texture. 
Shrinks  and  checks  considerably  when  drying.  Easily  worked. 
Durable  when  exposed  to  the  weather.  The  heartwood  is  dark 
and  the  sapwood  light-brown  in  color.  Used  for  cabinet  work, 
cooperage,  ties,  telegraph  poles,  and  exposed  heavy  construction. 

Poplar  (Whitewood). — Soft,  very  close  and  straight  grained, 
brittle.  Shrinks  excessively  in  drying.  Warps  and  twists  very 
much  but  does  not  split  when  dry.  Easily  worked.  Light- 
yellow  to  white  color.  Used  for  vehicles,  wooden  instruments, 
toys,  furniture,  finishing,  etc. 

Lignum-VitcB. — Very  hard,  heavy,  resinous,  has  a  soapy 
feeling,  and  is  difficult  to  split  and  work.  Color,  rich  yellow-brown 
varying  to  almost  black.  Used  for  small  turned  articles,  tool 
handles,  and  sheaves  of  block  pulleys. 

Teak. — Tropical  wood,  durable,  heavy,  hard,  elastic,  strong, 
and  easy  to  work.  When  seasoned  it  does  not  rack,  split,  shrink, 
or  alter  in  shape.  Aromatic  odor.  Heartwood  is  golden- 
brown  in  color,  seasoning  into  brown.  The  sapwood  is  white. 
Used  in  temples,  ships,  buildings,  and  for  structural  timbers. 
Can  be  used  in  contact  with  iron. 

Catalpa. — Light  weight,  soft,  weak,  elastic,  and  durable  in 
contact  with  the  soil.  Used  for  ties,  posts,  cabinet  work,  and 
interior  finishing. 

Eucalyptus. — Very    hard,    heavy,    strong,   tough,    and    close 


TIMBER  143 

grained.  Hard  to  split  after  it  is  dried.  Not  durable  in  contact 
with  the  soil.  Resembles  ash  and  hickory  in  appearance. 
Resists  attacks  of  marine  borers.  Used  for  wharf  piling,  lumber, 
parts  of  vehicles,  furniture,  flooring,  paving,  etc. 

Beech. — Hard,  heavy,  strong,  and  tough.  Not  durable  when 
exposed.  Subject  to  attack  by  insects.  Liable  to  check  in 
seasoning.  Takes  a  high  polish.  Color,  white  to  light-brown 
or  reddish.  Used  for  furniture,  interior  finish,  ship  building, 
and  carriage  making. 

188.  General    Characteristics  of    Some    Endogenous   Trees. 
Palmetto. — Lightweight.     Difficult    to    work    when    dry.     Very 
durable  under  water  as  it  resists  attacks  by  the  Teredo  and  borers. 
Color,  light-brown  with  dark-colored  fibers.     Used  for  piles  and 
wharves. 

Bamboo. — Hollow  stem  with  many  joints.  Many  branches, 
usually  small  ones.  Used  for  timbers,  columns,  masts,  poles, 
rafters,  water  pipes,  furniture,  split  bamboo  work,  etc. 

B.  PREPARING  THE  TIMBER 

189.  Logging. — Logging   may   be   said   to  be  the  process  of 
felling  the  trees,   trimming  off  the   branches  and  vegetation, 
cutting  the  trunks  and  limbs  to  proper  sizes,  and  transporting  the 
logs  to  the  sawmill.     The  trees  are  felled  by  means  of  axes  or 
saws  and  are  then  chopped  or  sawn  into  sizes  small  enough  to  be 
transported  to  the  sawmill.     The  methods  of  transportation  vary 
according  to  conditions.     If  the  sawmill  is  quite  close  to  the  forest, 
the  logs  may  be  rolled  downhill,  placed  on  sleds  drawn  by  horses, 
pulled  by  a  donkey  engine  and  windlass,  drawn  by  automobiles, 
carried  by  an  aerial  tramway,  floated  down  small  streams,  or 
carried  by  a  narrow-gage  logging  railway  to  the  mill.     If  the 
sawmill  is  some  distance  away,  the  logs  may  be  transported  by 
railway  or  assembled  in  rafts  and  floated  on  a  river  or  other 
waterway  to  the  mill. 

It  is  important  to  choose  the  proper  time  for  cutting  the  timber. 
In  the  spring  and  late  summer,  the  sapwood  contains  an  abun- 
dance of  moisture  with  starches,  sugars,  and  oils  in  solution,  all  of 
which  tend  to  hasten  the  decay  of  the  timber.  In  the  drier 
summer  months  and  in  the  winter,  the  growing  and  conducting 
cells  of  the  tree  are  less  active  or  altogether  dormant,  and  the  best 
wood  is  secured  if  the  timber  is  cut  during  those  seasons.  Oak  is 


144  MATERIALS  OF  CONSTRUCTION 

claimed  to  be  more  durable  if  it  is  cut  just  after  the  leaves  have 
fallen.  Hewn  lumber  is  thought  to  be  more  durable  than 
sawn  lumber.  Usually,  most  of  the  logging  operations  are  carried 
on  during  the  winter  months. 

190.  Sawing  the  Lumber. — Most  of  the  sawing  of  lumber  is 
done  in  sawmills  by  machine  driven  rotary  or  band  saws.  The 
manner  in  which  a  stick  of  lumber  is  sawed  from  the  log  has  a 


(a)  Flat  Sawed  (&)  Quarter  Sawed  (c)  Quarter  Sawed 

FIG.  75. — Methods  of  sawing  lumber. 

remarkable  influence  on  its  qualities  and  behavior.  The  kind 
of  sawing  is  determined  by  the  character  of  the  wood  and  the 
purpose  for  which  it  is  to  be  used. 

The  two  main  classes  of  sawing  are  flat  and  rift  sawing.  Flat 
sawing  consists  in  cutting  the  timber  tangential  to  the  annular 
rings.  Rift  (or  quarter)  sawing  is  cutting  the  boards  out  of  the 
log  in  such  a  manner  that  the  annular  rings  are  cut  through  as 
nearly  as  possible  in  a  radial  direction.  Quarter  sawing  is  done 
for  the  sake  of  the  beauty  of  the  grain  thus  obtained,  as  well 
as  to  expose  the  edge  of  the  hard  bands  of  the  summer  wood. 
Flat  sawing  and  rift  sawing  give  rise,  in  the  lumber  trade,  to  the 
terms  flat  grain  and  edge  grain  respectively.  Edge  grain  lum- 
ber does  not  sliver,  shrinks  and  checks  less,  and  wears  more 
evenly  and  smoothly  than  the  flat  grain  lumber. 

Ordinary,  or  bastard,  sawing  consists  of  cutting  the  log  into  a 
number  of  parallel  slices  and  then  trimming  the  edges  of  these 
slices  with  a  circular  saw.  In  ordinary  sawing,  some  of  the 
boards  will  be  flat  sawn,  some  quarter  sawn,  and  about  half  of 
them  will  be  neither  flat  nor  quarter  sawn  but  a  combination  of 
these. 

191.  Classification  of  Lumber. — All  material  sawn  from  logs 
for  structural  or  other  commercial  purposes  is  called  lumber. 
The  larger  sizes,  such  as  beams,  joists,  etc.,  are  called  timbers,  and 
these  timbers  are  usually  resawn  in  order  to  obtain  the  smaller 
sizes  of  lumber.  Lumber  is  furnished  in  all  sizes  and  dimensions 
such  as  are  suitable  for  the  work  at  hand. 


TIMBER  145 

The  term  "resawed  lumber"  is  applied  to  lumber  sawed  on  all 
four  sides.  Rough  edge  or  flitch  is  lumber  sawn  on  two  sides. 
Planed  resawed  lumber  is  called  dressed  lumber.  Dressed  planks 
and  boards  free  from  all  defects  are  called  clear.  Such  boards 
are  produced  in  regular  sizes  J^  in.  less  in  thickness  than  the 
sawed  lumber,  and  ranging  from  %  to  1%  in.  in  thickness. 

Sawed  timbers  shall  be  sound,  of  standard  size,  square  edged, 
and  straight;  and  they  shall  be  close  grained  and  free  from  de- 
fects, such  as  injurious  ring  shakes  and  cross  grain,  unsound  or 
loose  knots,  knots  in  groups,  decay,  or  other  defects  that  will 
materially  impair  the  strength. 

Rough  sawing  to  standard  size  shall  mean  that  the  timbers 
shall  not  be  over  Y±  in.  scant  from  the  actual  size  specified;  for 
instance,  a  12  by  12  timber  shall  not  measure  less  than  11%  by 
11%  in. 

Standard  dressing  shall  mean  that  not  more  than  y±  in.  shall 
be  allowed  for  dressing  each  surface;  for  instance,  a  12  by  12 
timber  after  being  dressed  on  four  sides  shall  not  measure  less 
than  UK  by  11^  in- 

The  standard  lengths  are  multiples  of  2  ft.,  running  from  10  to 
24  ft.  for  boards,  fencing,  dimension,  joists,  and  timbers.  Longer 
or  shorter  lengths  than  those  herein  specified  are  special  lengths. 
Special  and  fractional  lengths  shall  be  counted  as  of  the  next 
higher  standard  length. 

The  standard  widths  for  lumber  shall  be  multiples  of  1  in. 

All  sizes  1  in.  or  less  in  thickness  shall  be  counted  as  1  in.  thick. 

Flooring  shall  include  pieces  1,  1J^,  and  1J^  in.  thick  by  3  to  6 
in.  wide,  excluding  1%  by  6. 

Boards  shall  include  all  lumber  less  than  lj^  in.  thick  and  more 
than  6  in.  wide. 

Plank  shall  include  all  sizes  from  1J^  to  under  6  in.  in  thickness 
by  6  in.  or  over  in  width. 

Scantling  shall  include  all  sizes  exceeding  1^  in.  and  under  6 
in.  in  thickness,  and  from  2  to  under  6  in.  in  width. 

Dimension  sizes  shall  include  all  sizes  6  in.  and  more  in  thick- 
ness by  6  in.  and  more  in  width. 

Stepping  shall  include  all  sizes  from  1  to  2J^  in.  in  thickness  by 
7  in.  and  over  in  width. 

Rough  edge,  or  flitch,  shall  include  all  sizes  1  in.  and  more  in 
thickness  by  8  in.  and  more  in  width,  sawed  on  two  sides  only. 

192.  Defects  in  Lumber. — The  following  defects  are  adopted 
10 


146  MATERIALS  OF  CONSTRUCTION 

as  standard  by  the  American  Society  for  Testing  Materials. 
The  diameters  of  the  knots  and  holes  are  average  diameters. 

Knots. — A  sound  knot  is  one  which  is  solid  across  its  face  and 
which  is  as  hard  as  the  wood  surrounding  it ;  it  may  be  either  red 
or  black,  and  is  so  fixed  by  growth  or  position  that  it  will  retain 
its  place  in  the  piece  of  lumber. 

A  loose  knot  is  one  not  held  firmly  in  place  by  growth  or 
position. 

A  pith  knot  is  a  sound  knot  with  a  pith  hole  not  more  than  Y±  in. 
in  diameter  at  the  center. 

An  encased  knot  is  one  which  is  surrounded  wholly  or  in  part  by 
bark  or  pitch.  Where  the  encasement  is  less  than  J-^  of  an  inch 
in  width  on  both  sides,  not  exceeding  ^  the  circumference  of  the 
knot,  it  shall  be  considered  a  sound  knot. 

A  rotten  knot  is  one  that  is  not  so  hard  as  the  wood  it  is  in. 

A  pin  knot  is  a  sound  knot  not  over  %  in.  in  diameter. 

A  standard  knot  is  a  sound  knot  not  over  1^  in.  in  diameter. 

A  large  knot  is  a  sound  knot  more  than  1J^  in.  in  diameter. 

A  round  knot  is  one  which  is  oval  or  circular  in  form. 

A  spike  knot  is  one  sawed  in  a  lengthwise  direction. 

Wane. — Wane  is  bark,  or  the  lack  of  wood  from  any  cause,  on 
edges  of  timbers. 

Pitch  Pockets  are  openings  between  the  grain  of  the  wood  con- 
taining more  or  less  pitch  or  bark.  These  shall  be  classified  as 
small,  standard,  and  large  pitch  pockets.  A  standard  pitch 
pocket  is  one  not  over  %  of  an  inch  wide  or  3  in.  in  length.  A 
small  pitch  pocket  is  one  not  over  ^  of  an  inch  wide.  A  large 
pitch  pocket  is  one  over  %  of  an  inch  wide,  or  more  than  3  in.  long. 

A  Pitch  Streak  is  a  well  defined  accumulation  of  pitch  at  one 
point  in  the  piece.  When  the  pitch  is  not  sufficient  to  develop 
a  well  defined  streak,  or  where  the  fiber  between  grains  (the 
coarse  grained  fiber,  usually  termed  " spring  wood")  is  not 
saturated  with  pitch,  it  shall  not  be  considered  a  defect. 

Shakes  are  splits  or  checks  in  timbers  which  usually  cause  a 
separation  of  the  wood  between  the  annual  rings.  A  ring  shake 
is  an  opening  between  the  annual  rings.  A  through  shake  is 
one  which  extends  between  two  faces  of  a  timber. 

Rot,  Dote,  and  Red  Heart  are  forms  of  decay  which  may  be 
evident  either  as  a  dark  red  discoloration  not  found  in  sound  wood, 
or  by  the  presence  of  white  or  red  rotten  spots,  and  shall  be 
considered  as  defects. 


TIMBER  147 

193.  Natural  Seasoning  of  Lumber. — In  the  preparation  of 
lumber  for  construction  purposes,  it  is  necessary  to  expel  the 
sap  and  moisture  from  the  pores  of  the  wood  by  some  natural 
or  artificial  means.     This  process  is  called  seasoning.     It  has 
been  found  that  the  drier  the  timber,  the  less  likely  it  is  to 
shrink  and  decay. 

Natural  air  seasoning  consists  in  exposing  the  planks  and 
boards,  after  sawing,  to  a  free  circulation  of  air.  The  lumber  is 
placed  on  skids  in  large  square  piles  under  shelter  in  a  dry  place, 
the  layers  being  separated  by  three  or  four  narrow  strips  or  boards 
laid  in  the  opposite  direction.  The  lowest  layer  should  be  at 
least  2  ft.  from  the  ground.  At  frequent  intervals  the  decayed 
pieces  should  be  removed  and  the  lumber  replied.  The  time 
required  for  thorough  seasoning  varies  from  1  to  3  years,  depend- 
ing upon  the  character  of  the  wood,  the  purpose  for  which  it  is 
to  be  used,  and  its  dimensions. 

Water  seasoning  is  another  type  of  natural  seasoning  which 
consists  in  immersing  the  lumber  in  water.  The  soluble  sub- 
stances in  the  sap  wood  are  removed,  leaving  a  timber  that  is  less 
liable  to  warp  and  crack.  Water  seasoning  causes  the  heartwood 
to  become  brittle  and  lose  its  elasticity.  In  this  method  of 
seasoning,  the  timber  is  immersed  for  about  2  weeks  and  then 
removed  and  thoroughly  dried  with  an  excess  of  air.  If  im- 
mersed too  long,  the  wood  becomes  brashy  when  exposed  to  the 
air.  Water  seasoning  is  not  very  much  used. 

194.  Artificial  Seasoning  of  Lumber. — Artificial  seasoning  or 
kiln  drying  hastens  the  evaporation  of  the  moisture  and  the 
removal  of  the  sap,  but  it  produces  an  inferior  product  because  it 
causes  a  rapid  drying  of  the  surfaces  and  ends  of  the  material 
and  a  slow  or  imperfect  drying  of  the  interior.     This  weakens 
both  the  strength  and  the  elasticity  of  the  wood. 

The  timber  is  stacked  in  a  drying  kiln  and  exposed  to  a  current 
of  hot  air,  the  temperature  depending  upon  the  kind  of  lumber 
and  its  dimensions.  Sometimes  vacuum  pumps  are  used  in 
connection  with  the  heating.  The  temperature  usually  varies 
from  about  100  degrees  Fahrenheit  for  oak  to  about  200  degrees 
Fahrenheit  for  pine.  The  time  required  depends  upon  the 
thickness  of  the  lumber.  About  4  days  are  required  for  1  in. 
pine,  spruce,  or  cedar  boards.  Hard  woods  are  usually  dried 
in  air  from  3  to  6  months  and  then  placed  in  the  drying  kiln 
from  6  to  10  days. 


148  MATERIALS  OF  CONSTRUCTION 

When  rapidly  dried  in  a  kiln,  oak  and  other  hard  woods  tend 
to  become  "  case-hardened "  as  the  outer  parts  dry  and  shrink 
before  the  interior  parts  have  a  chance  to  do  the  same.  Thus 
there  is  a  firm  shell  of  dry,  shrunken,  and  usually  checked  wood 
about  the  interior.  When  the  interior  drys,  it  tends  to  become 
checked  along  the  medullary  rays.  Lumber  that  has  been  properly 
air  dried  will  not  case-harden  when  placed  in  a  kiln. 

195.  Shrinkage  of  Lumber. — When  a  short  piece  of  wood  fiber 
dries,  it  shrinks;  its  walls  become  much  thinner  and  the  cavity 
becomes  greater,  but  the  length  of  the  fiber  remains  about  the 
same.  A  thick-walled  fiber  shrinks  more  than  a  thin-walled  one. 
As  most  of  the  fibers  in  a  tree  are  parallel  to  its  length,  the  length 
of  a  timber  will  not  change  appreciably,  but  the  cross  section  will 
shrink  when  the  timber  is  seasoned.  The  medullary  rays  have  an 
effect  on  the  shrinkage  of  the  cross-section,  the  wood  in  the  cross- 
section  shrinking  more  at  right  angles  to  the  rays  than  parallel 
to  them,  due  to  the  fact  that  the  rays  themselves  shrink  in  cross- 
section  but  not  in  length.  Hence,  the  greatest  shrinkage  in 
lumber  will  take  place  tangentially  to  the  annular  rings,  a  little 
less  shrinkage  will  take  place  in  a  direction  radially  to  the  annular 
rings,  while  the  shrinkage  in  the  longitudinal  direction  of  the 
tree  will  be  inappreciable.  The  shrinkage  of  the  fibers  tangen- 
tially to  the  annular  rings  is  known  as  circumferential  shrinkage. 
Some  woods  shrink  much  more  unevenly  than  others.  The 
harder  timbers  are  more  compact  in  structure,  with  thicker  cell 
walls,  and,  therefore,  produce  the  greatest  shrinkage. 

Quarter-sawed  lumber  will  shrink  less  than  flat-sawed  lumber. 
A  combination  of  quarter  and  flat  sawing  will  cause  the  lumber 
to  shrink  unevenly,  thus  causing  a  warped  surface.  Flat  sawing 
produces  lumber  that  checks  and  cracks  to  a  greater  extent  in 
drying  than  rift  sawed  lumber  does. 

If  the  outer  fibers  of  a  timber  dry  out  much  faster  than  the 
inner  fibers  do,  the  timber  will  tend  to  become  checked  and 
cracked.  This  tendency  toward  checking  and  cracking  may  be 
reduced  by  driving  S-irons,  etc.  in  the  ends  of  the  timbers. 

If  a  board  shrinks  unevenly,  it  will  become  warped.  This 
may  be  due  to  the  fibers  on  one  side  drying  out  faster  than  the 
ones  on  the  other  side,  uneven  drying,  sawing  in  such  a  way  that 
the  shrinkage  will  be  more  in  some  directions  than  in  others,  or 
due  to  the  structure  of  the  board  itself. 

The  opposite  effect  to  shrinkage  is  produced  by  the  absorption 


TIMBER 


149 


of  moisture,  and  precautions  must  be  taken  when  applying  timber 
to  construction  work  to  allow  for  this  expansion,  such  as  expan- 
sion joints  in  a  wood-block  pavement.  A  roadway  40  ft.  wide 
(constructed  of  wood  blocks)  has  been  observed  to  expand  8  in. 


FIG.  76. — Effects  of  shrinkage.         FIG.  77. — Formation  of  checks. 
(Bull.  10,    U.  S.  For.  Div.)  (Bull.  10,   U.  S.  For.  Div.) 

The  longitudinal  shrinkage  of  timber  is  usually  less  than 
1  per  cent.  The  change  in  volume  of  the  timber  is  due  to  the 
radial  and  tangential  shrinkage,  and  expressed  in  percentages 
is  approximately  twice  the  figures  given  in  the  following  table, 
as  the  shrinkage  takes  place  in  two  directions  in  approximately 
equal  amounts.  The  following  are  average  values  for  shrinkage 
in  width: 


PEH  CENT 
SHRINKAGE 

3 
4 
4 


SHRINKAGE  OF  THE  WIDTH  OF  WOOD 

KIND  OF  WOOD 

Light  conifers  (soft  pines,  spruce,  cedar,  cypress) . . . 

Heavy  conifers  (hard  pine,  tamarack) 

Honey  locust,  box  elder,  wood  of  old  oaks 

Ash,   elm,    walnut,   poplar,   maple,    beech,   cherry, 

sycamore 5 

Basswood,  birch,  chestnut,  blue  beech,  young  locust  6 

Hickory,  young  oak  (especially  red  oak) up  to  10 

C.  DURABILITY  AND  DECAY  OF  LUMBER 

196.  Durability  and  Decay  of  Lumber  in  General. — The  life 
of  timber  depends  upon  the  way  in  which  it  is  felled,  seasoned, 
and  worked.  The  timber  is  subject,  in  both  its  growing  and 


150  MATERIALS  OF  CONSTRUCTION 

converted  states,  to  decomposition  and  attack  by  animal  and 
vegetable  life.  Trees  should  be  felled  when  the  growing  and 
conducting  cells  are  less  active  or  are  dormant.  Seasoning 
increases  the  life  of  timber  by  removing  the  sap  and  moisture. 
In  structural  work  the  timber  should  be  protected  as  much  as 
possible  from  the  attack  of  agencies  that  cause  decay. 

The  agencies  which  produce  the  decay  of  wood  are:  alternate 
moisture  and  dryness,  heat  and  confined  air,  bacteria  and  fungi, 
insects  and  worms.  Well  seasoned  wood  in  a  uniform  state  of 
moisture  or  dryness  and  well  ventilated  should  never  decay. 
Timber  that  is  kept  constantly  immersed  in  water  may  soften  or 
weaken  but  it  will  not  decay.  Elm,  elder,  oak,  and  birch  possess 
great  durability  when  kept  constantly  immersed. 

Dryness  and  ventilation  are  the  best  preventives  of  the  decay 
of  timber  used  for  construction  purposes.  Wood  that  has  been 
kept  dry  has  been  known  to  last  for  hundreds  of  years,  though  it 
finally  became  brittle  and  lost  most  of  its  strength.  In  construc- 
tion work  it  is  important  that  timber  be  kept  completely  im- 
mersed in  water  or  else  kept  in  a  fairly  dry  condition  and  well 
ventilated.  Water  should  be  prevented  from  collecting  in  the 
joints,  and  important  structural  timbers  should  be  protected 
from  weather  conditions  when  practical. 

197.  Dry  Rot  in  Lumber. — Dry  rot  is  directly  caused  by  the 
fermentation  and  breaking  down  of  the  chemical  compounds  of 
the  wood,  due  to  the  introduction  of  a  certain  fungus  in  the 
presence  of  a  little  moisture.  These  lower  organisms  excrete 
ferments  which  dissolve  out  parts  of  the  cell  walls,  thus  causing 
a  crumbling  of  the  wood.  The  growth  of  this  fungus  is  stimulated 
by  moderate  warmth,  presence  of  dampness,  and  lack  of  venti- 
lation. Dry  rot  is  often  found  in  ill-ventilated  places,  such  as  the 
wall  pockets  at  the  ends  of  floor  timbers,  and  in  the  core  of 
timber  columns  in  mill  construction.  The  decomposition  is  often 
hastened  by  the  use  of  unseasoned  wood. 

Dry  rot  is  indicated  by  a  swelling  of  the  timber  and  a  change  in 
the  color,  the  wood  gradually  becoming  covered  with  mold  and 
emitting  a  musty  odor.  Sometimes  reddish  or  yellowish  spots 
appear  on  the  timber,  and  the  fibers  are  gradually  reduced  to  a 
powder.  Dry  rot  is  especially  dangerous  as  it  destroys  the 
timber  in  which  it  originates  and  also  tends  to  spread  to  adjacent 
woodwork.  It  is  difficult  to  eradicate,  when  it  is  once  estab- 
lished, the  only  remedy  being  to  remove  all  of  the  fungus  and 


TIMBER  151 

disinfect  the  wood.     Actual  contact  is  not  necessary  for  the 
spreading  of  dry  rot. 

198.  Wet  and  Common  Rot. — Wet  rot  appears  only  when  the 
wood  is  kept  damp  or  is  subject  to  alternate  dryness  and  moisture. 
It  will  not  take  place  if  the  wood  is  thoroughly  seasoned  and  the 
further  absorption  of  moisture  prevented.     The  decay  is  caused 
by  the  moisture  which  dissolves  out  the  substance  of  the  cell 
walls  of  the  sap  wood.     Wet  rot  spreads  by  actual  contact  only. 
Wood  cut  in  the  spring  and  early  fall  is  especially  subject  to  wet 
rot.     The  remedy  is  to  remove  ah1  of  the  rotten  parts  of  the 
timber  and  keep  the  remainder  dry  and  well  ventilated. 

Common  rot  is  shown  by  the  presence  of  external  yellow  spots 
on  the  ends  of  timber  sticks  and  often  by  a  yellowish  dust  in  the 
checks  and  cracks,  especially  where  the  timbers  are  in  contact 
with  each  other.  The  cause  of  common  rot  is  improper  seasoning 
in  badly  ventilated  sheds. 

199.  Injurious  Insects. — The  larvae  of  many  insects  are  de- 
structive to  wood.     The  living  trees  are  attacked  by  some,  and 
the  felled  trees  and  lumber  by  others. 

Some  of  the  common  insects  attacking  the  wood  of  living  trees 
are  the  oak  and  chestnut  timber  worms,  locust  borers,  carpenter 
worms,  ambrosia  beetles,  turpentine  beetles  and  borers,  and  the 
white  pine  weavil. 

Round  timbers  with  the  bark  on  are  subject  to  attack  by  the 
insects  mentioned  above,  and  especially  'by  the  round-headed 
borers,  timber  worms,  and  ambrosia  beetles. 

Seasoned  and  finished  hardwood  lumber  is  especially  subject  to 
attack  by  powder  post  beetles. 

Construction  timbers  are  often  seriously  injured  by  wood 
boring  larvae,  termites,  black  ants,  carpenter  bees,  and  powder 
post  beetles. 

The  damage  is  caused  by  the  insects,  or  their  larvae,  eating  or 
" boring"  holes  in  the  timbers,  thus  breaking  the  continuity  of  the 
fibers  and  reducing  the  cross-sectional  areas. 

200.  Marine  Wood  Borers. — The  Teredo  or  ship  worm  belongs 
to  the  mollusk  species  and  is  the  marine  borer  which  is  the  most 
active,  and  destructive  to  wood.     It  bores  its  way  in  lumber 
usually  in  a  direction  parallel  to  the  grain  and  lines  the  hole  with 
a  calcareous  deposit  as  it  progresses.     These  worms  vary  much 
in  size,  some  of  the  largest  being  about  half  an  inch  in  diameter 
and  4  or  5  ft.  long.     They  live  in  clear  salt  water,  preferably  of 


152  MATERIALS  OF  CONSTRUCTION 

the  warmer  climates,  and  are  more  active  near  calcareous  shores. 
They  work  from  the  ground  up  to  the  half -tide  level. 

The  lycoris  fucata  is  a  little  worm  with  many  legs  something 
like  a  centipede.  It  crawls  up  the  piles  or  timbers  inhabited  by 
the  Teredo,  enters  the  hole,  finds  and  eats  the  Teredo,  and  then 
lives  in  the  hole. 

The  xylotrya  also  belongs  to  the  mollusk  species,  and  is  similar 
to  the  Teredo  in  structure  and  mode  of  life. 

The  limnora,  or  gribble,  is  a  small  crustacean  resembling  a 
wood  louse  and  is  about  the  size  of  a  grain  of  rice.  It  can  swim, 
crawl,  and  jump.  Both  air  and  water  are  required  for  its 
existence;  consequently,  its  attacks  on  wood  are  confined  to  a 
space  between  the  high-  and  low-water  marks.  It  devours  the 
wood  at  the  rate  of  1  to  3  in.  a  year,  and  is  found  in  both 
warm  and  cold  water. 

D.  PROPERTIES  OF  TIMBER 

201.  Strength  of  Timber  in  General. — The  mechanical  proper- 
ties of  wood  are  very  variable,  not  only  between  different  kinds 
of  trees,  but  between  trees  of  the  same  kind,  and  even  between 
specimens  cut  from  different  parts  of  the  same  tree.  In  estimat- 
ing the  properties  of  timber  the  following  things  should  be  con- 
sidered— correct  identification  of  the  species  and  variety,  age  and 
rate  of  growth  of  the  trees,  position  of  test  specimen  in  the  tree, 
moisture  content,  and  freedom  of  test  specimens  and  commercial 
timbers  from  defects. 

In  general,  the  results  of  tests  have  shown  that: 

The  influence  of  defects  is  very  marked.  Defects  tend  to 
lower  the  ultimate  strength.  Knots  and  cross  grains  lower  the 
elastic  limit. 

Tests  on  small  specimens  usually  give  results  that  are  at  least 
50  per  cent  greater  than  the  results  obtained  from  tests  on  large 
specimens. 

Large  checks  and  seasoning  cracks  weaken  the  wood. 

In  general,  the  strength  of  wood  varies  with  the  specific 
gravity. 

Timber  treated  with  creosote,  tannin,  zinc  chloride,  etc.  is 
usually  weaker  than  untreated  timber. 

Dry  timber  is  much  stronger  (about  75  per  cent)  than  wet  or 
green  timber. 


TIMBER  153 

The  strength  parallel  to  the  grain  is  different  than  the  strength 
perpendicular  (across)  to  the  grain. 

The  strength  of  timber  under  any  kind  of  a  permanent  load  is 
only  about  one-half  of  the  strength  found  by  short  time  tests. 

Rapid  loading  in  tests  will  give  higher  results  than  slow  loading. 

In  general,  the  larger  the  percentage  of  summer  wood,  the 
stronger  the  timber. 

In  general,  the  strength  of  wood  varies  with  the  number  of 
annular  rings  per  inch. 

It  must  be  remembered  that  the  percentage  of  moisture  is  the 
greatest  factor  influencing  the  strength  of  timber;  hence,  the 
percentage  of  moisture  in  the  specimens  tested  should  always  be 
given. 

202.  Influence  of  Moisture  Content  in  Timber. — Moisture 
has  a  very  great  influence  upon  the  strength  of  timber,  probably 
more  than  any  other  factor.  The  strength  and  weight  of  timber 
depend,  to  a  large  extent,  upon  the  number  of  fibers  per  unit 
area  of  cross  section;  hence,  the  more  fibers  per  unit  area  the 
heavier  and  stronger  the  wood.  Absorption  of  moisture  by  the 
wood  causes  the  fibers  to  swell  in  diameter  and  thus  the  number 
of  fibers  per  unit  cross  sectional  area  are  decreased  and  .the 
wood  is  not  so  strong.  Further,  moisture  tends  to  weaken 
the  cells  and  make  them  less  firm  and  strong.  Results  of  tests 
have  shown  that,  in  the  seasoning  of  Southern  pines  from  green 
wood  (33  per  cent  of  moisture)  to  dry  wood  (about  10  per  cent 
of  moisture),  there  were  variations  of  over  75  per  cent  in  the 
average  strength,  the  strength  increasing  with  the  decrease  in 
moisture. 

The  strength  decreases  with  increase  in  the  moisture  content 
up  to  the  point  where  the  cell  walls  become  completely  saturated. 
This  limit  is  between  20  and  30  per  cent  for  most  woods.  The 
addition  of  more  moisture  to  the  wood  fills  the  cavities  and  causes 
no  further  swelling  of  the  cell  walls  and  has  practically  no  effect 
upon  the  strength. 

The  amount  of  moisture  contained  in  ordinary  dry  lumber  is 
about  15  per  cent,  and  this  value  varies  greatly  with  the  tem- 
perature and  weather.  So-called  "dry"  wood  usually  has  as 
much  as  8  per  cent  of  moisture,  while  green  and  wet  woods  con- 
tain over  30  per  cent.  It  is  practically  impossible  to  obtain 
perfectly  dry  wood.  Wood  is  said  to  be  dry  when  it  has  been 
dried  to  a  constant  weight  (the  variation  in  weight  for  a  period  of 


154  MATERIALS  OF  CONSTRUCTION 

24  hours  being  less  than  ^  of  1  per  cent)  in  an  oven  where 
the  temperature  was  kept  approximately  at  212  degrees 
Fahrenheit. 

203.  Tensile  Strength  of  Timber. — The  tensile  strength  of 
timber  is  not  of  much  importance  except  as  it  is  involved  in 
transverse  loading.     In  construction,  timber  is  rarely  ever  sub- 
jected to  pure  tensile  stresses,  due  to  the  difficulty  of  designing 
proper  end  fastenings. 

Failure  in  tension  across  the  grain  is  due  to  the  tearing  or 
pulling  apart  of  the  wood  fibers  longitudinally.  The  tensile 
strength  across  the  grain  is  only  a  small  part  (Jf  Q  ^°  Mo) 
of  the  tensile  strength  parallel  to  the  grain. 

Failure  in  tension  along  the  grain  is  due  to  the  transverse  or 
oblique  tearing  apart  of  the  wood  fibers.  That  is,  the  fibers 
are  rarely  pulled  in  two,  but  they  are  usually  pulled  out  from 
between  the  .others.  Knots,  cross  grain,  medullary  rays,  and 
other  defects  weaken  the  timber  in  tension. 

The  proportional  elastic  limit  of  wood  in  tension  along  the 
grain  is  usually  between  60  and  75  per  cent  of  the  ultimate 
strength. 

204.  Gompressive    Strength    of    Timber. — The    compressive 
strength  of  timber  is  important  as  timbers  are  very  frequently 
used  as  columns  and  compression  members  in  various  structures. 

In  compression  along  the  grain;  the  fibers  act  like  a  number 
of  hollow  columns  bound  together.  When  failure  occurs,  the 
fibers  tend  to  bend  or  buckle  over  each  other  and  shear  off.  The 
compressive  strength  along  the  grain  depends  upon  the  density  of 
the  wood,  the  stiffness  and  continuity  of  the  wood  fibers,  adhe- 
sion between  the  fibers,  seasoning,  moisture  content,  straightness 
of  grain,  and  defects. 

The  proportional  elastic  limit  in  compression  along  the  grain 
is  usually  between  60  and  75  per  cent  of  the  ultimate  strength. 

In  compression  across  the  grain  the  fibers  fail  by  flattening. 
The  strength  depends  primarily  on  the  density  of  the  wood, 
though  many  of  the  other  factors  have  some  influence.  The 
strength  across  the  grain  is  from  %  to  Y±  of  that  along  the  grain. 

205.  Transverse  Strength  of  Timber. — The  transverse  strength 
of  timber  is  important  as  timbers  are  often  used  as  beams  and 
joists  in  structural  work. 

The  strength  of  timber  in  cross  bending  depends  largely  upon 
the  compressive,  tensile,  and  shearing  strengths.  Consequently, 


TIMBER  155 

the  transverse  strength  of  timber  depends  upon  the  same  factors 
as  the  tensile  and  compressive  strengths  do. 

Timber  beams  rarely  have  a  final  failure  in  compression,  though 
the  initial  failures  are  nearly  always  in  compression.  Final 
tension  failures  are  quite  common,  especially  if  the  beam  is  long 
compared  with  its  thickness  or  if  there  are  defects  on  the  tension 
side.  A  large  proportion  of  the  failures  occur  by  horizontal 
shear,  especially  if  the  beam  is  short  and  thick. 

The  " elastic  limit"  in  cross  bending  is  usually  between  66 
per  cent  and  75  per  cent  of  the  ultimate  strength.  A  load  in 
excess  of  the  elastic  limit  will  cause  a  beam  to  break  if  left  loaded. 

The  modulus  of  elasticity  in  cross  bending  is  a  variable  quantity 
because  the  load  deflection  curve  is  not  a  straight  line,  even  as 
far  as  the  elastic  limit.  The  value  of  the  modulus  of  elasticity 
in  cross  bending  is  about  the  same  as  that  in  compression. 

Stiffness  is  the  ability  of  a  beam  to  resist  cross-bending  loads 
without  having  large  deflections.  The  transverse  modulus  of 
elasticity  may  be  considered  as  a  measure  of  the  stiffness. 
Straight  grained  lumber  is  stiffer  than  knotty  or  cross-grained 
pieces,  and  dry  wood  is  about  one  and  a  half  times  as  stiff  as 
green  or  wet  wood.  In  general,  the  heavier  the  wood,  the  stronger 
and  stiffer  it  is. 

206.  Shearing  Strength  of  Timber. — The  resistance  to  shear 
across  the  grain  is  from  four  to  ten  times  that  along  the  grain. 
The  shearing  strength  is  less  in  wet  woods  than  in  dry  woods, 
and  it  is  reduced  by  defects,  such  as  knots,  checks,  cracks,  etc. 
The  shearing  strength  along  the  grain  is  very  small  and  depends 
upon  the  adhesion  of  the  wood  fibers  to  each  other,  the  straight- 
ness  of  grain,  the  medullary  rays,  etc.     The  shear  across  the 
grain  is  approximately  half  of  the  compressive  strength  along 
the  grain  and  depends  upon  the  same  factor. 

The  shearing  strength  of  timber  is  important,  especially  in  beams. 

207.  Cleavability  and  Flexibility  of  Timber. — Cleavability  is 
the  resistance  of  wood  to  splitting,  as  with  an  axe  or  other  tool. 
Elastic  woods  split  more  easily  than  others,  while  woods  with 
great  hardness  and  transverse  tensile  strength  are  hard  to  split. 

Wood  splits  naturally  along  the  two  normal  planes  and  a  little 
more  readily  along  the  radius.  The  weight  of  the  wood  has  but 
little  effect  on  the  cleavage.  Defects,  especially  knots  and  cross 
grains,  and  the  presence  of  moisture,  increase  the  resistance  of  the 
wood  to  splitting. 


156  MATERIALS  OF  CONSTRUCTION 

Flexibility  is  the  ability  of  the  wood  to  bend  very  much  without 
breaking.  Hard  wood  is  usually  more  flexible  than  soft  wood. 
Moisture  softens  the  wood  and  makes  it  more  flexible,  while  knots 
and  other  defects  make  it  less  flexible. 

208.  Hardness    and    Toughness    of    Timber. — Hardness    is 
usually  measured  by  the  penetration  of  a  ball  or  a  steel  plunger 
under  a  load.     The  hardness  is  closely  related  to  the  shearing 
strength   across   the   grain.     Heavy   wood  is  harder  than  light 
wood.     Seasoning  tends  to  increase,  and  moisture  to  decrease,  the 
hardness.     Placing     the     annular     rings     in  a  vertical  position 
appears  to  help  the  wood  to  resist  indentation. 

A  tough  wood  is  a  wood  that  is  strong  and  flexible  and  able  to 
resist  shocks  and  blows.  Toughness  is  often  measured  in  impact 
tests  by  finding  the  amount  of  work  required  to  cause  rupture. 
Wood  which  offers  a  high  resistance  to  tension  and  longitudinal 
shear  and  which  is  capable  of  suffering  a  distortion  of  more  than 

3  per  cent  in  tension  and  compression  is  usually  tough. 

209.  Miscellaneous  Properties  of  Timber. — The  approximate 
chemical  composition  of  all  woods  when  dry  is  nearly  uniform, 
and  consists,  by  weight,  of  the  following  elements:  49  percent 
carbon,  6  per  cent  hydrogen,  44  per  cent  oxygen,  and  1  per  cent 
ash.     The    weight  per  cubic  foot  for  most  dry  woods  varies 
between  25  and  60  Ib.     A  few  woods  are  lighter  and  some  are 
heavier  than  these  values.     Moisture  increases  the  weight  per 
cubic  foot  very  considerably. 

The  coefficient  of  linear  expansion  per  degree  Fahrenheit  and 
for  temperatures  between  35  and  60  degrees  Fahrenheit  varies  as 
follows:  parallel  to  the  fibers  from  0.0000014  to  0.0000054; 
and  perpendicular  to  the  fibers,  from  0.0000019  to  0.0000034. 

210.  Factors  of  Safety  and  Safe  Working  Loads  for  Timber.— 
The  factors  of  safety  (and  safe  working  stresses)  vary  according  to 
the  kind  of  stress  and  kind  of  loading  and  also  according  to  the 
judgment   of   various   engineers.     In   designing,    only   the  net 
section  of  the  dressed  timber  should  be  considered. 

The  following  factors  of  safety  for  variable  loads  are  considered 
good  practice:  10  for  tension,  5  for  compression  with  grain, 

4  for  compression  across  grain,  6  for  extreme  fiber  stress  in  cross 
bending,  2  for  modulus  of  elasticity  in  cross  bending,  and  4  for 
shear. 

For  steady  loads,  these  factors  of  safety  may  be  decreased 
33  per  cent  (corresponding  to  an  increase  of  50  per  cent  in  the  unit 


TIMBER 


157 


' 


II 


II 


ec ec ic •* co w <N ec co « co 


gooooooooo; 


Rl 

— « s 

oil 


«3  >O  t»  CO  »O  O  »O  >O 


.  00  CO  t»  00  00  W  t»  CO  1C  T}*  00  Oi  ^  l>-  "3   "500 


II 


)«COO>C'C 


**  CO  «C  Tf  T}<  *#  CO  "4*  CO  CO  CO   US  »C  •*  1C  1C  1C  »C  «C  •«*<  CO  CO  CO  CO  CO  ^  CO 


*>  4>  I- 

j<ar«a 


o  : 


.  W 
'.S 

:& 


:S 


158  MATERIALS  OF  CONSTRUCTION 

working  stresses).  These  factors  of  safety  are  too  low  for 
timbers  containing  large  or  loose  knots. 

For  continuous  heavy  loading,  loading  causing  a  reversal  in 
stress,  or  for  apparently  sound  old  timbers,  the  allowable  unit 
stresses  (safe  working  loads)  should  be  about  80  per  cent,  or 
those  obtained  by  the  use  of  the  factors  of  safety  for  variable 
loads. 

211.  Properties  of  Timber. — The  preceding  table  gives  the 
properties  of  timber  containing  from  15  to  20  per  cent  of  moisture : 

The  above  values  are  average  values  for  dry  commercial 
timber.  Small  specimens  or  specimens  of  exceptional  quality 
may  give  test  results  50  or  60  per  cent  higher.  Specimens  of  poor 
quality  (containing  serious  defects)  or  specimens  from  a  weaker 
species  of  wood  may  give  test  results  less  than  those  given  above. 
Also,  green  wood  or  wood  containing  a  large  amount  of  water  may 
give  results  below  those  given  above. 

To  obtain  the  working  stress,  divide  the  ultimate  by  a  suitable 
factor  of  safety,  depending  upon  the  kind  of  load  (see  article  on 
"Factors  of  Safety"  and  "Safe  Working  Loads  for  Timber"). 


E.  SELECTION  AND  INSPECTION  OF  TIMBER 

212.  Selection  of  Timber. — When  timber  is  selected  for  a 
special  purpose  it  should  be  investigated  and  the  kind  chosen 
which  appears  to  meet  most  fully  the  particular  requirements  of 
the  case. 

For  framing  timbers,  woods  should  be  selected  that  are  plenti- 
ful and,  consequently,  cheap,  and  which  can  be  obtained  in  large 
dimensions.  Sometimes  it  is  important  to  consider  extra  strength 
and  durability. 

For  wood  that  is  to  be  buried  in  the  ground  (either  in  whole  or 
in  part)  or  is  to  be  used  for  piling,  durability  is  the  chief  considera- 
tion, although  the  question  of  cost  must  be  often  considered. 

For  wood  that  is  to  be  used  in  water  (either  in  whole  or  in  part) 
for  piles,  wharves,  etc.,  durability  and  freedom  from  attack  by 
borers  are  the  most  important  considerations. 

For  outside  finishing,  ease  of  working  and  freedom  from  warp- 
ing and  checking  are  the  most  important  requirements.  The 
wood  should  be  able  to  stand  the  wear  from  exposure 
(weathering) . 


TIMBER  159 

For  floors,  the  wearing  qualities  (and  sometimes  the  appear- 
ance) are  the  chief  considerations. 

For  interior  finishing  and  decorating,  the  color  and  grain  of  the 
wood  and  its  ability  to  take  a  polish  and  finish  often  decide  the 
choice. 

213.  Inspection  of  Timber. — Timber  is  inspected  to  determine 
the  quality  of  the  stock  and  the  dimensions  of  the  pieces.  All 
condemned  pieces  must  be  plainly  marked  with  paint  or  a  brand- 
ing iron.  Sometimes,  in  the  case  of  large  timbers,  all  accepted 
pieces  are  marked  with  a  paint  or  a  branding  iron  which  is  differ- 
ent from  that  used  in  marking  the  condemned  pieces. 

Strong  and  durable  timber  possesses  the  following  characteris- 
tics: 

It  is  obtained  from  the  slowest  growing  trees,  as  indicated  by 
the  narrowness  of  the  annular  rings. 

The  best  timber  comes  from  the  heart  of  the  tree,  and  should 
include  no  sap  wood. 

Wood  containing  the  least  amount  of  resin  or  sap  in  its  pores 
is  the  most  durable. 

The  wood  should  be  uniform  in  appearance,  straight  in  fiber, 
free  from  large  and  dead  knots,  and  free  from  all  flaws,  shakes, 
and  blemishes. 

Freshly  cut  sound  timber  smells  sweet,  and  shows  a  firm  and 
bright  surface  with  a  silky  luster  when  it  is  planed. 

The  surface  should  never  be  woolly,  and  the  wood  should  not 
clog  the  teeth  of  the  saw. 

In  highly  colored  woods,  darkness  of  color  generally  indicates 
strength  and  durability. 

Sound  timber,  when  lightly  struck  or  scratched  at  one  end, 
transmits  the  sound  to  the  ear  placed  at  the  other  end,  even 
though  the  timbers  are  as  long  as  50  ft. 

Sound  timber  is  sonorous  when  struck,  while  decaying  timber 
gives  forth  a  dull  sound. 

A  dull,  chalky  appearance  and  a  disagreeable  odor  are  signs  of 
bad  timber. 

In  the  absence  of  the  usual  external  signs,  dry  rot  may  be 
detected  by  boring  test  holes  in  the  wood  and  then  examining 
the  appearance  and  odor  of  the  wood  dust. 

Timber  containing  defects,  such  as  knots,  checks,  cracks,  pitch 
pockets,  bark,  excess  sapwood,  etc.  not  allowed  by  the  specifica- 
tions, should  be  rejected. 


160  MATERIALS  OF  CONSTRUCTION 

Timber  should  be  measured  (length,  breadth,  and  thickness) 
to  see  if  it  is  of  the  proper  dimensions  (see  article  on  "Classifica- 
tion of  Lumber"). 

F.  PRESERVATION  OF  TIMBER 

214.  Preservation  of  Timber  in  General. — The  life  of  timber 
can  be  prolonged  somewhat  by  thorough  seasoning,  but  a  better 
way  is  to  inject  into  the  timber  some  substances  such  that,  while 
they  are  not  appreciably  harmful  to  the  timber,  will  act  as  poisons 
toward  the  fungi,  borers,  etc.  that  cause  the  decay  of  wood. 
The  materials  most  commonly  used  are  creosote  (dead  oil  of 
coal  tar),  zinc  chloride,  copper  sulphate,  and  bichloride  of 
mercury  (corrosive  sublimate). 

There  are  three  general  methods  of  injecting  the  " preserva- 
tives" into  the  timber.  The  first  or  pressure  process  (sometimes 
called  the  pressure-tank  process)  makes  use  of  force  pumps,  air 
compressors,  etc.,  to  secure  the  pressure  desired.  Practically  all 
of  the  special  processes  are  pressure  processes. 

The  non-pressure,  or  open-tank,  process  uses  atmospheric 
pressure  only.  One  method  is  to  take  thoroughly  seasoned  wood, 
immerse  it  from  1  to  6  hours  in  a  bath  of  hot  liquid,  and  then 
change  it  quickly  to  a  cold  bath.  This  change  causes  a  contrac- 
tion of  the  air  and  moisture  in  the  timber  and  allows  the  entrance 
of  the  preservative.  Another  method  is  first  to  heat  the  timber  in 
an  oven  and  then  suddenly  immerse  it  in  a  cold  bath  of  the  pre- 
serving liquid. 

The  third  general  method  consists  of  painting  the  timber  with 
one  or  more  coats  of  the  preservative  by  means  of  a  brush.  It  is 
known  as  the  " brush"  process.  The  painting,  with  coal  tar,  of 
timbers  that  are  to  be  placed  in  the  ground  is  a  common  example 
of  this  method. 

The  pressure  process  is  thought  to  decrease  slightly  the  strength 
and  elasticity  of  the  timber,  but  the  other  two  general  processes 
seem  to  have  no  bad  effects,  as  the  coating  of  the  cell  walls  and 
fibers  with  a  preservative  should  not  injure  them.  However,  a 
too  concentrated  solution  of  some  of  the  preservatives  might 
cause  chemical  dissociation  of  the  wood.  Preliminary  steaming 
at  too  high  pressures  or  for  too  long  a  time  weakens  the  timber. 
The  limits  for  pressure  and  time  are  about  as  follows :  40  Ib.  per 
square  inch  for  3  hours,  30  Ib.  per  square  inch  for  4  hours,  and 
20  Ib.  per  square  inch  for  5  hours. 


TIMBER  161 

215.  Creosote  Processes  for  Preservation  of  Timber. — 
Creosote  has  been  found  to  be  the  best  of  all  of  the  preservative 
coatings  for  timber  under  practically  all  conditions.  It  is 
especially  effective  against  the  Teredo  and  other  sea  worms  and 
borers.  Creosoting  is  not  suitable  for  wood  that  is  to  be  used  for 
interior  or  decorative  work.  Any  of  the  three  general  methods 
may  be  used  for  creosoting,  but  the  pressure  process  is  the  best. 

The  open-tank  process  consists  of  immersing  the  timbers  in  a 
bath  of  creosote  and  allowing  them  to  soak  for  a  few  days  before 
they  are  removed  and  used.  This  process  is  not  very  satisfactory 
as  the  penetration  of  the  oil  is  small. 

BethelPs  process  of  creosoting  is  probably  the  most  important 
process  in  use.  It  is  briefly  as  follows:  The  timber  is  placed  in  a 
large  cylinder;  steamed  thoroughly  for  a  few  hours  to  evaporate 
the  sap ;  then  a  pump  removes  the  sap  and  steam  and  produces  a 
partial  vacuum;  after  which  the  cylinder  is  filled  with  creosote 
oil  (distilled  from  coal  tar)  heated  to  about  150  degrees  Fahren- 
heit and  under  a  pressure  of  about  175  Ib.  per  square  inch. 
About  5  Ib.  of  oil  per  cubic  foot  of  timber  are  required.  The 
length  of  time  is  24  hours.  Green  timber  requires  from  12  to  18 
Ib.  of  oil  per  cubic  foot  of  timber. 

Seeley's  process  is  a  modification  of  Bethell's  process.  The 
timber  is  immersed  in  creosote  oil  at  a  temperature  of  212  to 
300  degrees  Fahrenheit  for  a  time  sufficient  to  expel  the  moisture. 
The  hot  oil  is  then  drawn  off  and  replaced  by  a  cold  bath.  The 
amount  of  oil  absorbed  is  about  4  Ib.  per  cubic  foot  of  wood. 

In  the  Breant  process  the  timber  is  placed  in  a  vertical  cylinder 
and  the  liquid  is  let  in  almost  to  the  top.  A  partial  vacuum  is 
then  produced  by  an  air  pump,  after  which  the  valve  is  closed 
and  the  liquid  forced  in  until  a  pressure  of  about  10  atmospheres 
is  reached.  The  time  required  for  impregnation  is  about  6 
hours. 

In  the  A.  C.  W.  process  the  method  is  like  the  Bethell  process 
except  that  an  air  pressure  of  15  Ib.  per  square  inch  is  applied 
after  the  vacuum  and  maintained  while  the  creosote  is  admitted 
so  as  to  prevent  unequal  absorption  during  the  filling.  Then  a 
pressure  of  100  Ib.  per  square  inch  is  applied  until  the  desired 
amount  of  penetration  is  reached,  after  which  the  creosote  is 
withdrawn  and  air  is  forced  in  under  a  pressure  of  about  70 
Ib.  per  square  inch. 

In  the  boiling  process  (used  principally  for  Douglas  fir)  the 
11 


162  MATERIALS  OF  CONSTRUCTION 

timber  is  placed  in  a  cylinder  containing  creosote  oil  at  a  tem- 
perature a  little  above  212  degrees  Fahrenheit  and  kept  there  for 
a  period  varying  from  a  few  hours  to  2  days.  Then  a  pressure 
of  about  120  Ib.  per  square  inch  is  applied,  the  temperature  is 
allowed  to  drop,  and  the  preservative  forced  into  the  wood. 

In  the  Ruping,  or  empty-cell,  process  the  timber  is  air  dried 
before  being  placed  in  the  cylinder.  Air  is  admitted  at  a  pressure 
of  75  Ib.  per  square  inch  and  then  the  creosote  is  admitted  at 
about  85  Ib.  per  square  inch,  after  which  the  pressure  is  increased 
up  to  about  225  Ib.  per  square  inch  to  force  the  oil  into  the  timber. 
When  the  pressure  is  removed,  the  compressed  air  in  the  wood 
forces  out  most  of  the  oil,  leaving  only  a  coating  around  the 
cell  walls.  This  process  gives  a  very  high  penetration  of  oil 
with  but  little  absorption. 

The  Lowry  process  is  the  same  as  the  Ruping  process,  except 
that  no  compressed  air  is  used  before  admitting  the  creosote 
under  pressure. 

In  the  Kreodone  process  the  timber  is  first  sterilized  by  subject- 
ing it  to  a  dry  heat  of  240  degrees  Fahrenheit  for  8  hours. 
The  remainder  of  the  process  is  like  the  Bethell  process,  except 
that  Kreodone  (an  oil  derived  from  creosote)  is  used  instead  of 
the  creosote.  The  absorption  is  about  12  Ib.  of  oil  per  cubic  foot 
of  wood. 

In  the  creo-resinate  process  a  mixture  of  creosote  and  resin, 
containing  from  50  to  70  per  cent  creosote,  is  used  instead  of  the 
creosote.  The  process  is  similar  to  the  Bethell  process,  except 
that  a  dry  heat  is  used  instead  of  the  steam  bath  before  the 
vacuum. 

216.  Zinc  Chloride  Pressure  Processes  for  Preservation  of 
Timber. — Burnett's  process  is  the  most  important  zinc  chloride 
process.  It  is  briefly  as  follows:  The  timber  is  placed  in  a  closed 
metal  cylinder;  a  20-in.  vacuum  is  produced;  steam  is  added  at 
a  pressure  of  25  Ib.  per  square  inch  for  about  4  hours;  then  the 
steam  is  removed  and  a  second  vacuum  produced;  a  zinc  chloride 
solution  is  added  at  a  temperature  of  150  degrees  Fahrenheit  and 
under  a  pressure  of  about  135  Ib.  per  square  inch.  About  0.24 
Ib.  of  zinc  per  cubic  foot  of  timber  is  required.  The  time  taken 
is  about  10  hours.  The  zinc  solution  contains  about  43  per 
cent  of  zinc,  2  per  cent  of  impurities,  and  55  per  cent  of  water. 

In  the  Allardyce  process  a  2  or  3  per  cent  zinc  chloride  solution 
is  first  forced  into  the  timber  by  a  process  like  Burnett's  process 


TIMBER  163 

and  then  creosote  is  injected.  The  creosote  remains  on  the 
outside,  thus  protecting  the  soluble  zinc  chloride  in  the  interior. 
About  12  Ib.  of  the  zinc  chloride  solution  and  3  Ib.  of  creosote 
are  required  per  cubic  foot  of  timber. 

In  the  card  process  the  preserving  liquid  is  a  3  to  5  per  cent 
solution  of  zinc  chloride  containing  about  15  or  20  per  cent  of 
creosote.  The  process  is  similar  to  that  of  BethelFs.  As  the 
two  preservatives  will  not  mix,  a  pump  is  used  to  keep  them  in 
a  mechanical  mixture. 

The  Wellhouse  process  consists  of  first  steaming  the  timber 
in  a  cylinder  for  a  few  hours  and  then  adding  a  solution  of  zinc 
chloride  and  glue  under  pressure,  after  which  tannin  is  injected. 
The  glue  combines  with  the  tannic  acid  in  the  wood  and  is  pre- 
cipitated while  the  wood  retains  the  zinc.  The  tannin  is  added 
to  precipitate  the  excess  of  glue. 

217.  Vulcanizing  Process  for  Preserving  Timber. — Vulcaniz- 
ing consists  of  rendering  the  sap  insoluble  and  undecomposable 
by  the  application  of  heat.     This  process  tends  to  make  the 
timber  less  combustible  besides  preserving  it.     The   wood  is 
placed  in  a  closed  vessel  and  under  pressure  to  prevent  the  vapori- 
zation of  the  sap  when  it  is  heated.     The  heat  is  gradually 
applied  and  the  pressure  is  gradually  increased  as  the  tempera- 
ture rises.     A  temperature  of  400  degrees  Fahrenheit  is  sufficient 
to  vulcanize  ordinary  woods.     The  time  required  varies  from 
about  8  hours  for  soft  woods  to  from  10  to  20  hours  for  hard 
woods. 

218.  Some  Other  Pressure  Processes  for  Preserving  Timber. 
Boucherie's  (copper  sulphate)  process  is  the  addition  of  copper 
sulphate  under  a  pressure  of  15  Ib.  per  square  inch  and  in  the 
proportion  of  1  Ib.  of  copper  to  10  gal.  of  water.     This  method 
is  used  very  much  in  Germany.     The  wood  should  be  green. 

Kyan's  process  (sometimes  called  "Kyanizing")  consists  of 
impregnating  the  timber  with  bichloride  of  mercury  (corrosive 
sublimate).  The  solution  is  in  the  proportion  of  1  Ib.  of  mercury 
bichloride  to  50  Ib.  of  water. 

Payne's  process  consists  of  injecting  sulphate  of  iron  into  the 
wood  in  a  vacuum,  followed  by  an  injection  of  a  solution  of 
sulphate  of  lime  or  soda.  This  process  also  makes  the  wood 
incombustible. 

Thilmany's  process  is  the  impregnation  of  the  wood  with  zinc 
or  copper  sulphate.  The  method  is  about  the  same  as  BethelTs 


164  MATERIALS  OF  CONSTRUCTION 

creosoting  process,  except  that,  instead  of  adding  creosote,  a 
solution  of  zinc  sulphate  (or  copper  sulphate)  is  added  under  a 
pressure  of  about  90  Ib.  per  square  inch.  After  the  residue  of 
sulphate  is  removed  from  the  cylinder,  a  1  per  cent  solution  of 
barium  chloride  is  added  under  pressure.  Green  wood  is  pre- 
ferred for  this  process. 


CHAPTER  X 

PIG  IRON 
A.  DEFINITION  OF  PIG  IRON  AND  ORES  OF  IRON 

219.  Definition  of  Pig  Iron. — As  pure  iron  is  not  found  free  in 
nature,  it  is  necessary  to  reduce  the  ores  of  iron.     The  product 
obtained  by  the  reduction  of  iron  ores  in  a  blast  furnace  is  called 
pig  iron.     These  iron  ores  usually  consist  of  compounds  of  iron 
and    oxygen    with    some    other    impurities.     The    important 
commercial  ores  contain  from  25  to  70  per  cent  of  iron. 

220.  Ores  of  Iron. — The  ores  of  iron  in  the  order  of  their 
importance  are  as  follows: 

Red  Hematite  (Fe2O3)  varies  from  black  to  brick-red  in  color 
and  contains  about  70  per  cent  of  iron  when  pure.  The  presence 
of  impurities  reduces  this  percentage  to  about  50  or  60  per  cent. 
The  specific  gravity  of  the  red  hematite  is  about  5.3;  its  streak 
is  always  red.  This  ore  often,  occurs  as  an  earthy  ore  which  is 
easily  mined  and  handled.  It  is  found  on  all  of  the  continents 
and  is  the  most  important  ore  in  the  manufacture  of  iron. 

Brown  Hematite  or  Limonite  (Fe2O3  +  nH2O)  varies  in  color 
from  a  brownish-black  to  a  yellowish-brown,  usually  occurs  in 
massive  form,  and  is  softer  and  lighter  than  the  red  hematite. 
Limonite  ore  is  a  red  hematite  containing  about  14.5  per  cent  of 
chemically  combined  water.  Its  streak  is  yellowish-black. 
Its  specific  gravity  varies  from  3.6  to  4.0.  When  pure,  this  ore 
contains  about  60  per  cent  of  iron,  but  the  commercial  ore  usually 
contains  from  40  to  50  per  cent  of  iron.  Limonite  is  found 
principally  in  the  United  States. 

Magnetite  (FeaO4) ,  the  richest  and  hardest  iron  ore,  is  a  hard 
black  mineral  occurring  in  a  granular  or  massive  form.  It 
contains  72.4  per  cent  of  iron  when  pure;  has  a  specific  gravity  of 
about  5.2;  has  a  black  streak;  is  almost  as  magnetic  as  pure  iron; 
and  is  often  contaminated  with  oxides  of  silicon,  phosphorus,  and 
titanium.  At  present  there  is  no  economical  method  for  separat- 
ing the  titanium  oxide  from  the  iron  ore  and,  consequently,  the 
ores  having  this  impurity  in  them  are  practically  worthless. 
Magnetite  is  found  principally  in  Sweden  and  the  United  States. 

165 


166  MATERIALS  OF  CONSTRUCTION 

Iron  Carbonate  (FeC03),  often  called  siderite  or  spathic  ore,  is 
gray  or  brown  in  color  and  contains  about  48  per  cent  of  iron 
when  pure.  Ordinarjr  ore,  due  to  the  presence  of  impurities, 
contains  only  from  30  to  40  per  cent  of  iron.  Its  specific  gravity 
varies  from  3.7  to  3.9.  If  exposed  to  the  weather  for  some  time, 
this  ore  will  change  to  limonite  or  red  hematite.  Iron  carbonate 
is  found  in  England,  the  United  States,  and  other  countries. 

Pyrite  (FeS2)  contains  about  47  per  cent  of  iron  when  pure. 
It  is  golden-yellow  in  color;  has  a  greenish  or  brownish-black 
streak;  and  a  specific  gravity  between  4.8  and  5.2.  As  this  ore 
must  be  desulphurized  before  being  used,  very  little  of  it  is  used 
at  the  present  time. 

221.  Ore  Mining. — The  soft  earthy  ores  that  lie  on  the  surface 
or  near  the  surface  of  the  ground  are  mined  by  steam  shovels 
in  an  open  cut.     The  soil  is  first  removed  from  the  top  of  the  ore 
bed,  and  then  the  steam  shovel  loads  the  ore  into  ore  cars  which 
convey  the  ore  to  the  blast  furnace. 

The  hard  ores  must  be  drilled  and  blasted  before  they  can  be 
transported  to  the  blast  furnace.  It  costs  more  to  mine  the  hard 
ores  than  the  soft  ones,  but  a  certain  proportion  of  hard  ore  is 
required  for  the  successful  operation  of  the  blast  furnace. 

If  the  ore  veins  are  underground,  the  mining  must  be  carried  on 
by  underground  methods.  The  expense  depends  upon  the 
conditions  present. 

222.  Preliminary  Treatment  of  Iron  Ores. — The  rich  soft  ores 
(red  hematite)  require  no  preliminary  treatment  before  they  are 
fed  to  the  blast  furnace,  but  the  other  ores  need  to  be  treated. 

Crushing  to  proper  size  is  necessary  for  the  hard  ores.  Jaw  or 
gyratory  crushers  are  usually  used  for  this  purpose. 

Ores  containing  clay  and  dirt  are  washed  to  remove  these 
impurities. 

Calcination,  or  preliminary  heating,  is  used  to  remove  the 
water  or  carbon  dioxide  from  the  ores.  Sometimes  some  of  the 
gangue  is  oxidized  at  the  same  time.  The  heater  used  is  a 
vertical  furnace  something  like  a  mixed  feed  lime  kiln. 

If  the  ore  contains  sulphur,  it  may  be  roasted  to  remove  this 
impurity.  Only  a  moderate  heat  is  required. 

If  the  ore  is  magnetic,  or  has  been  made  magnetic  by  calci- 
nation, a  magnetic  separator  may  be  used  to  separate  the  ore 
from  much  of  its  gangue. 

Ores  may  be  divided  into  bessemer  or  non-bessemer  ores, 


PIG  IRON 


167 


168 


MATERIALS  OF  CONSTRUCTION 


according  to  their  phosphorus  content.  Ores  in  which  the 
phosphorus  content  exceeds  Mooo  Part  of  the  iron  content  are 
called  non-bessemer  ores. 

B.  MANUFACTURE  OF  PIG  IRON 

223.  The  Blast  Furnace. — Practically  all  of  the  iron  used  today 
is  first  reduced  from  the  ores  to  pig  iron  by  means  of  the  blast 


FIG.  79. — Blast  furnace  with  charging  mechanism.      (Illinois  Steel  Company). 

furnace.  This  furnace  is  a  big  circular  steel  shell,  usually  about 
100  ft.  high  and  22  ft.  in  diameter,  lined  with  silica  firebrick.  A 
furnace  of  this  size  has  a  capacity  of  about  450  tons  of  pig  iron  in 
a  24-hour  day.  About  900  tons  of  good  ore  are  required  to 
produce  this  450  tons  of  iron. 


PIG  IRON 


169 


The  bottom  part  of  the  furnace,  called  the  hearth  or  crucible,  is 
about  7  or  8  ft.  high,  and  its  purpose  is  to  hold  the  molten  metal. 
At  the  lower  part  of  the  hearth  there  is  a  tap  hole  for  drawing  off 
the  molten  iron.  About  halfway  up  the  hearth  there  is  another 
hole,  called  the  cinder  notch,  which  is  used  to  draw  off  the  slag. 
When  not  in  use,  these  holes  are  plugged  with  clay  balls.  Just 
below  the  top  of  the  hearth  there  is  a  ring  of  nozzles  or  tuyeres 


FIG.  80. — Blast  furnace  plant.     (Illinois  Steel  Co.) 

piercing  the  hearth  linings.  These  tuyeres  are  connected  on  the 
outside  to  a  large  air  pipe  called  the  bustle  pipe.  The  tuyeres 
admit  the  hot-air  blast  to  the  furnace. 

The  part  of  the  furnace  above  the  hearth  is  called  the  bosh. 
This  is  the  hottest  part  of  the  furnace  and  it  has  to  be  cooled  by 
some  means  such  as  spraying  water  against  the  outer  surface  or 
by  the  use  of  a  water  jacket  full  of  running  water.  The  bosh  is 
about  12  ft.  high. 

The  part  of  the  furnace  between  the  bosh  and  the  bell  and 
hoppers  is  called  the  stack.  This  stack  is  divided  into  three 
parts,  called  the  lower  inwall,  middle  inwall,  and  top.  The 
height  of  the  stack  is  about  50  or  60  ft. 

The  top  of  the  blast  furnace  is  provided  with  a  double  bell  and 
hopper  for  charging  the  furnace  with  fuel,  flux,  and  ore.  The 


170 


MATERIALS  OF  CONSTRUCTION 


materials  are  first  charged  into  the  upper  hopper.  They  fall  into 
the  lower  hopper  when  the  upper  bell  is  lowered.  Lowering  the 
lower  bell  allows  the  materials  in  the  lower  hopper  to  spread  in 
an  even  layer  on  the  materials  in  the  furnace. 


FIG.  81. — Sectional  view  of  blast  furnace  showing  details  of  hearth  and  bosh. 
(Harbison-Walker    Refractories    Co.) 

The  hot  waste  gases,  generated  during  the  operation  of  the 
furnace,  are  removed  from  the  furnace  by  means  of  a  pipe  called 
the  downtake.  This  pipe  enters  the  furnace  just  below  the  lower 
bell.  The  downtake  is  provided  with  an  extra  pipe  and  valve 


PIG  IRON  171 

(called  the  bleeder)  which  serve  as  a  relief  if  the  gas  pressure 
gets  too  high.  At  the  bottom  of  the  downtake,  there  is  a  dust 
catcher  which  removes  all  of  the  solid  particles  in  the  gas  passing 
through  the  downtake. 

224.  Accessories  of  the  Blast  Furnace. — The  mechanical 
equipment  used  in  connection  with  the  blast  furnace  includes 
bins  for  holding  the  ore,  fuel,  and  flux;  charging  equipment; 
blowing  engines  and  auxiliaries;  hot-blast  stoves;  and  usually 
some  apparatus  for  drying  the  blast. 

The  charging  equipment  consists  of  a  double  inclined  track  and 
skips  or  small  cars  which  carry  the  materials  from  the  bins  to  the 
top  of  the  furnace.  These  cars  are  loaded  by  gravity  at  the  bins, 
and  they  dump  the  materials  automatically  in  the  upper  hopper. 

The  blowing  engines  are  usually  gas  engines  of  about  2,000 
horse  power  which  will  deliver  from  45,000  to  60,000  cu.  ft.  of  air 
per  minute  at  a  pressure  of  from  15  to  30  Ib.  per  square  inch. 
These  engines  use  the  washed  waste  gases  from  the  furnace  as 
fuel. 

The  hot-blast  stoves  are  steel  shells,  about  as  high  as  the  blast 
furnace,  lined  with  firebrick  and  divided  into  a  number  of  vertical 
compartments.*  There  are  usually  four  of  these  stoves  for  each 
furnace.  The  stoves  are  first  heated  by  the  escaping  burned 
gases  from  the  blast  furnace  and  are  then  used  to  heat  the  air 
blast,  when  on  its  way  to  the  furnace  from  the  blowing  engines,  to 
a  temperature  of  about  1,000  degrees  Fahrenheit.  Usually  one 
stove  is  used  to  heat  the  blast  while  the  others  are  being  heated 
by  the  exhaust  gases. 

As  ordinary  air  contains  about  1  Ib.  of  water  per  1,000 
cu.  ft.,  it  has  been  found  economical  first  to  dry  the  air  before  admit- 
ting it  to  the  blowing  engines.  This  drying  is  accomplished 
by  first  cooling  the  air  down  below  its  dew  point  by  means  of 
refrigerating  machinery.  This  cooling  causes  a  condensation  of 
a  large  part  of  the  moisture  in  the  air.  The  drying  of  the  air  blast 
permits  of  a  saving  of  about  15  per  cent  in  the  amount  of  fuel 
required  in  the  blast  furnace  to  reduce  the  ore. 

225.  The  Fuel. — The  fuel  used  in  a  blast  furnace  must  provide 
the  necessary  heat  and  also  act  as  a  reducing  agent.  This  fuel 
must  be  strong  and  porous  and  capable  of  producing  an  intense 
heat  without  leaving  an  ash  which  has  a  high  content  of  phos- 
phorus or  sulphur.  The  fuels  that  are  used  in  blast  furnaces  are 
coke,  coal,  and  charcoal. 


172  MATERIALS  OF  CONSTRUCTION 

Coke  is  the  solid  residue  obtained  by  the  distillation  of  the 
volatile  matter  in  certain  grades  of  bituminous  coal,  called 
"  coking  coals."  The  weight  of  coke  produced  is  about  two- 
thirds  of  that  of  the  coal  used.  At  present,  coke  is  the  most 
used  and  the  most  satisfactory  fuel  for  blast  furnaces.  Compared 
with  anthracite  coal  and  charcoal,  coke  is  first  in  firmness,  second 
in  structure,  and  third  in  ash.  The  choice  of  fuel  in  any  locality 
depends  much  upon  the  relative  cost,  charcoal  usually  being 
the  most  expensive. 

Anthracite  coal  can  be  used  successfully  in  the  blast  furnace 
without  preparation.  It  tends  to  become  broken  into  fine  pieces 
upon  heating,  is  less  firm  than  coke,  and  has  less  ash  than  coke 
has  but  more  than  charcoal. 

Bituminous  coals  are  the  least  desirable  to  use  as  they  soften 
and  become  broken  up,  when  heated,  besides  containing  more 
ash  than  any  of  the  other  fuels. 

Charcoal  has  the  least  ash  and  the  best  structure  of  all  the 
fuels,  but  is  less  firm  than  coke  or  anthracite.  Charcoal  is  the 
carbonaceous  residue  remaining  after  wood  has  been  heated  and 
the  volatile  matter  driven  off.  In  making  charcoal,  air  must  not 
come  in  contact  with  the  wood  while  it  is  being  heated.  Charcoal 
is  fragile,,  light,  and  very  porous. 

226.  The  Flux. — A  flux  is  a  substance  which  will  combine  with 
the  earthy  parts  of  the  iron  ore  and  the  ash  of  the  fuel  and 
produce  a  fusible  slag  which  may  be  separated  from  the  metallic 
iron.     Acid    gangues    require    basic    fluxes,     and    vice    versa. 
Practically   all   of  the  gangues  are  acid    in  character;    hence, 
basic  fluxes  are  nearly  always  required. 

Limestone  is  the  cheapest  form  of  a  basic  flux,  and  it  is  used 
oftener  than  any  other.  The  limestone  should  be  very  pure  as 
acid  impurities  reduce  the  efficiency.  Sometimes  dolomitic 
magnesium  limestones  are  used  if  the  high-calcium  limestones 
are  hard  to  obtain.  The  presence  of  the  magnesium  appears 
to  have  no  bad  effects  on  the  flux,  and  some  think  that  magnesium 
improves  the  quality  of  the  flux. 

Quicklime  could  be  used  instead  of  limestone  for  a  flux,  but  its 
advantages  are  more  than  offset  by  the  increase  in  cost. 

227.  Operation  of  the  Blast  Furnace. — In  reducing  an  iron  ore, 
the  blast  furnace  has  the  following  five  important  functions  to 
perform : 

1.  The  deoxidation  of  the  iron  ore. 


PIG  IRON 


173 


2.  The  carburization  of  the  iron. 

3.  The  melting  of  the  iron. 

4.  The  making  of  a  fusible  slag  and  then  melting  it. 

5.  The  separation  of  the  molten  iron  from  the  molten  slag. 
The  charge  of  a  blast  furnace  consists  of  about  one-half  ore, 

one-third  fuel,  and  one-sixth  flux  deposited  in  the  furnace  in 
rotation  and  continually  so  as  to  keep  the  level  of  the  materials 


GRAPHIC  RCMCUNTATIOM  Of  THC  WEIGHT  OF  SuBSTANCIS  IN  THE  (LAST   FURNACE. 


FIG.  82. — Chart  showing  changes  occurring  in  a  blast  furnace  charge.  Figures 
represent  Ibs.  per  2240  Ibs.  of  pig-iron.  Horizontal  distances  are  proportional 
to  weights.  (From  Campbell.) 

about  7  or  8  ft.  below  the  bottom  of  the  lower  bell  and  hopper. 
Different  grades  of  ores  are  often  mixed  so  as  to  secure  the  proper 
proportioning  of  the  chemical  elements. 

The  air  blast  enters  the  furnace  through  the  tuyeres  and  rises 
through  the  various  layers  of  the  charge  to  the  top.  The  oxygen 
of  the  blast  combines  with  the  carbon  in  the  fuel  and  forms  CO 
with  the  evolution  of  much  heat,  the  temperature  being  about 
3,500  degrees  Fahrenheit  at  the  top  of  the  hearth.  Passing 
through  a  layer  of  ore,  the  CO  takes  oxygen  from  the  ore  and 
forms  CO2  besides  heating  the  ore.  Reaching  another  layer  of 
fuel,  the  CO2  takes  carbon  from  this  fuel  and  forms  CO  which 
again  changes  to  CO2  when  the  next  layer  of  ore  is  reached. 
This  process  is  continued  until  the  gas,  consisting  of  N  from  the 
air  blast  and  CO  and  CO2,  arrives  at  the  top  of  the  furnace,  where 
it  passes  off  through  the  downtake. 


174  MATERIALS  OF  CONSTRUCTION 

During  the  process  of  reduction  of  the  iron  ore,  a  thin  layer  of 
carbon  is  deposited  upon  the  brickwork  of  the  furnace.  This 
layer  protects  the  brick  from  rapid  destruction  due  to  the  cor- 
rosive action  of  the  slag. 

The  gas  from  the  furnace,  after  passing  off  through  the  down- 
take  and  being  cleaned,  is  used  for  heating  the  hot-blast  stoves 
and  for  operating  the  blower  engines  and  other  engines  used  for 
supplying  the  power  required  to  operate  the  machinery  of  the 
plant. 

As  the  fresh  ore  descends  in  the  furnace,  it  loses  its  oxygen  and 
absorbs  much  heat  and  some  carbon  from  the  rising  gases.  The 
carbon  makes  the  iron  more  fusible  and  it  soon  begins  to  melt  and 
to  run  down  through  the  fuel  and  slag  to  the  hearth,  absorbing 
some  silicon  and  sulphur  on  the  way. 

The  limestone  flux  loses  CO2  near  the  center  of  the  furnace, 
leaving  the  infusible  calcium  oxide  which  combines  with  the 
alumina,  silica,  and  earthy  bases  in  the  ore  and  forms  a  fusible 
slag  which  floats  on  the  top  of  the  molten  metal  in  the  hearth. 
Some  of  the  sulphur  present  combines  with  the  lime,  and  the 
resulting  calcium  sulphide  is  dissolved  in  the  slag. 

Whenever  necessary,  the  slag  is  drawn  off  through  the  cinder 
notch.  This  slag  can  be  used  as  an  aggregate  in  making  concrete 
and  as  a  raw  material  in  the  manufacture  of  cement,  mineral 
wool,  and  paint. 

When  sufficient  molten  iron  has  collected  in  the  hearth,  it  is 
drawn  off  through  the  tap  hole,  skimmed  of  its  slag,  and  is  either 
cast  into  pigs  or  conveyed  in  a  molten  condition  to  a  steel  plant. 

228.  Use  of  the  Electric  Furnace  in  Reducing  Iron  Ores. — 
Electric  furnaces  have  been  successfully  used  for  the  commercial 
reduction  of  iron  ores  in  localities  where  electricity  is  cheap 
and  the  proper  fuels  are  expensive.  As  only  about  two-ninths 
or  one-third  as  much  carbon  is  required  with  the  electric  furnace 
as  with  the  ordinary  blast  furnace,  there  is  a  great  saving  of  fuel. 
However,  the  cost  of  electrical  heat  is  usually  more  than  the  cost 
of  heat  produced  by  the  combustion  of  fuel. 

The  electric  furnace  that  has  been  used  the  most  is  of  the 
" resistance"  type  which  uses  electrodes  that  project  into  the 
charge  or  bath. 

A  very  high  quality  of  pig  iron  is  produced  by  the  electric 
furnace,  which  is  an  important  consideration  in  the  making  of 
very  high  grade  steel. 


PIG  IRON  175 

229.  Making  the  Pigs. — A  "pig"  of  cast  iron  is  generally  semi- 
cylindrical  in  form,  about  5  in.  in  width,  36  in.  in  length,  and  100 
Ib.  in  weight. 

Formerly,  the  pig  iron  was  cast  in  sand  beds  which  consisted 
of  a  series  of  depressions  molded  in  a  bed  of  silica  sand.  The 
molten  iron  was  withdrawn  from  the  blast  furnace  through  the 
tap  hole,  the  slag  skimmed  off,  and  the  iron  allowed  to  flow 
through  channels  to  the  pig  molds.  When  the  iron  had  solidified, 
the  iron  in  the  pig  molds  was  broken  away  from  that  in  the  chan- 
nels, and  then  the  iron  in  the  channels  was  broken  into  suitable 
lengths  by  the  use  of  sledge  hammers.  The  channels  are  often 
called  "  sows."  At  the  present  tune,  most  of  the  pig  iron  is  cast  in 
a  pig-molding  machine.  Such  a  machine  consists  essentially  of  a 
number  of  steel  molds  fastened  to  an  endless  chain.  The 
molten  iron  is  carried  from  the  blast  furnace  in  a  ladle  and  poured 
into  the  molds  as  they  are  carried  past  by  the  endless  chain. 
The  molds  are  carried  through  a  water  bath  which  solidifies  the 
pigs,  and  then  the  pigs  are  dumped  from  the  molds  into  a  pile 
or  into  a  car  for  shipment.  As  the  molds  return  toward  the 
charging  ladle,  they  are  sprayed  with  lime  water  to  prevent  the 
molten  iron  from  sticking  to  them. 


C.  CLASSIFICATION  AND  USES  OF  PIG  IRON 

230.  Classification  of  Pig  Iron. — Following  are  four  methods  of 
classifying  pig  iron: 

1.  Pig  iron  may  be  classified  according  to  the  method  of 
manufacture  into  coke  pig,  charcoal  pig,  and  anthracite  pig. 

2.  The    second  method  is  based  on  the  chemical  composition. 
There  are  four  divisions:  silicon  pig  which  has  a  high  silicon 
content;    low    phosphorus    pig;    special   low    phosphorus    pig; 
and    special  pigs    such  as    speigeliesen,    ferromanganese,    ferro- 
chrome,  etc. 

3.  For  commercial  purposes,  pig  iron  may  be  graded  by  the 
color,  hardness,  and  character  of  the  fracture  into  nine  divisions  : 
No.  1  Foundry,  No.  2  Foundry,  No.  3  Foundry,  No.  1  Soft,  No.  2 
Soft,  Silver  Gray,   Gray  Forge,   Mottled,  and  White.     No.   1 
Foundry  is  the  most  open  grained,  soft,  gray  iron  and  is  largely 
granular  in  fracture.     The  other  grades  gradually  pass  from  the 
soft  gray  iron  into  the  hard  white  iron.     Formerly,  this  classifica- 


176 


MATERIALS  OF  CONSTRUCTION 


tion  was  much  used  but  at  the  present  time  most  of  the  pig  iron  is 
purchased  by  chemical  analysis. 

4.  This  is  the  best  classification  and  is  according  to  the  pro- 
posed use  of  the  pig  iron.     There  are  five  divisions: 

1.  Bessemer  Pig. — For  acid  bessemer  or  acid-open  hearth  proc- 

esses of  making  steel. 

2.  Basic  Pig. — For  basic  bessemer  or  basic  open  hearth-processes 

of  making  steel. 

3.  Malleable  Pig. — For  malleable  cast  iron. 

4.  Foundry  Pig. — For  gray  cast  iron. 

5.  Forge  Pig. — An  inferior  foundry  pig  used  for  the  manufacture  of 

wrought  iron. 

The  purchase  of  these  grades  is  practically  based  on  the 
chemical  analysis.  The  following  table  gives  the  specified  limits. 
In  general,  the  carbon  content  varies  from  2  to  4  per  cent  and 
the  manganese  content  from  0.10  to  1.75  per  cent. 

CHEMICAL  CONTENTS  OF  SOME  PIG  IRON 


Kind  of  iron 

Silicon, 
per  cent 

Sulphur, 
per  cent 

Phosphorus, 
per  cent 

Remarks 

Bessemer  pig 

1   00  to  2  00 

0  05  or  less 

Not  over  0  10 

Graphitic    carbon 

Basic  pig  
Malleable  pig  
Foundry  pig  
Forge  pig  

Under    1.00 
0.75  to  2.00 
1.50  to  3.00 
Under    1.50 

Under       0.05 
Not  over  0.  05 
Not  over  0.  05 
Under       0.  10 

Not  specified 
Not  over  0.  20 
0.50    to    1.00 
Under       1  .  00 

combined  carbon, 
and  manganese 
may  be  specified. 

231.  Uses  of  Pig  Iron. — Pig  iron,  as  such,  has  no  structural 
uses  but  it  is  used  in  making  commercial  cast  iron,  malleable  iron, 
wrought  iron,  and  steel.  More  than  60  per  cent  of  pig  iron  is 
used  in  the  manufacture  of  steel  by  the  bessemer  and  open-hearth 
processes.  Approximately  3  per  cent  is  used  for  making  wrought 
iron  and  another  3  per  cent  for  making  malleable  cast  iron,  while 
about  20  per  cent  is  used  in  the  manufacture  of  gray  cast  iron. 

At  the  present  time  the  United  States  of  America  is  the  largest 
producer  and  user  of  pig  iron,  producing  and  using  about  one- 
half  of  the  world's  supply  of  iron  ore,  pig  iron,  and  iron  products. 
This  country  produces  annually  about  70,000,000  long  tons  of  iron 
ore  from  which  about  35,000,000  long  tons  of  pig  iron  are  made. 


CHAPTER  XI 


CAST  IRON 

A.  DEFINITIONS  AND  GENERAL  CLASSIFICATIONS 

232.  Definitions  of  Cast  Iron. — The  following  are  two  defini- 
tions of  cast  iron: 

Cast  iron  is  iron  containing  so  much  carbon,  or  its  equivalent, 
that  it  is  not  usefully  malleable  at  any  temperature. 

Cast  iron  is  a  saturated  solution  of  carbon  in  iron,  the  amount 
of  carbon  ordinarily  varying  from  2.0  to  4.0  per  cent,  depending 
upon  the  amounts  of  silicon,  sulphur,  phosphorus,  and  manganese 
present  in  the  solution. 

233.  General  Classification  of  Iron  and  Steel. — This  general 
classification  has  been  taken  from  the  American  Civil  Engineers' 
Pocket  Book. 

CLASSIFICATION  OF  IRON  AND  STEEL 


Material 

Per  cent 
of  carbon 

Specific 
gravity 

Properties 

Cast  iron  
Steel  
Wrought  iron  .  . 

2.  00  to  5.00 
0.10  to  1.50 
0.05  to  0.30 

Average  7  .  2 
Average  7  .  8 
Average  7  .  7 

Not  malleable  Not  temperable 
Malleable         Temperable 
Malleable          Not  temperable 

It  is  to  be  noted  that  the  percentage  of  carbon  alone  is  not 
enough  to  distinguish  steel  from  wrought  iron,  as  the  process  of 
manufacture  and  the  presence  of  different  chemical  elements 
both  have  some  influence  on  the  properties.  Also,  only  hard 
steels  can  be  tempered,  while  soft  steels  resemble  wrought  iron 
in  their  properties. 

234.  Howe's  Classification  of  Iron  and  Steel.— 
I.  Carbon  Class. — Properties  chiefly  determined  by  the  carbon 

content. 

A.  Weld   Metal.     Aggregated   from   a  pasty  mass  without 
later  fusion. 

1.  Wrought  Iron.     Carbon,  0.20  per  cent  or  less, 
12  177 


178  MATERIALS  OF  CONSTRUCTION 

2.  Blister  Steel.     Carbon,  0.20  to  2.20  per  cent. 
B.  Cast  or  Ingot  Metal.     Metal  that  is  initially  cast  and  is 
not  aggregated. 

1.  Steel.     Malleable  when  cast.     Carbon,  0.20  to  2.20 

per  cent. 

Low-carbon,  medium,  and  high-carbon  steel,  depending 
upon  the  carbon  content.  Not  dependent  on  the 
method  of  manufacture. 

2.  Cast  Iron.     Not  malleable.     Carbon  2.20  per  cent  or 

more. 
Gray   Cast   Iron.     Carbon  segregated  from  the  iron 

in  form  of  graphite. 

White  Cast  Iron.     Carbon  combined  with  the  iron. 
Mottled  Cast  Iron.     Mixture  of  gray  and  white  cast 

irons. 

3.  Malleable  Cast  Iron.     Cast  as  white  cast  iron  and  then 

made  malleable. 

II.  Alloy    Class. — Properties    chiefly    determined    by    elements 
other  than  carbon. 

A.  Special  or  Alloy  Steels.     Used  for  special  purposes  and 
usually  as  a  finished  product. 

B.  Ferro  Alloys.     Alloys  of  iron  used  principally  to  introduce 
certain  elements  into  steels. 

B.  MAKING  THE  MOLTEN  CAST  IRON 

235.  The  Materials. — Cast  iron  is  usually  made  by  remelting 
pig  iron  in  a  cupola  or  air  furnace  and  then  casting  it  in  its  final 
form  in  molds.  Sometimes  the  castings  are  made  from  molten 
pig  iron  taken  directly  from  the  blast  furnace. 

The  materials  used  are  pig  iron,  fuel,  and  flux.  Often  the  pig 
iron  from  several  blast  furnaces  is  mixed  so  as  to  secure  the  proper 
proportioning  of  the  chemical  elements  in  the  charge.  Some- 
times part  of  the  pig  iron  is  replaced  by  scrap  iron  (discarded 
castings),  old  or  broken  castings,  sprues,  etc. 

Coke  is  almost  always  used  for  fuel,  though  in  a  few  instances 
mixtures  of  coke  and  anthracite  coal  have  been  used  instead. 
The  amount  of  fuel  required  varies  according  to  the  castings  and 
the  furnaces.  The  cupola  requires  about  400  or  500  Ib.  of  coke 
per  ton  of  iron  for  small  thin  castings,  and  about  200  Ib.  of  fuel 
for  the  larger  castings.  Small  thin  castings  require  a  hotter 


CAST  IRON 


179 


metal  in  order  to  secure  good  results.     The  air  furnace  requires 
about  twice  as  much  fuel  per  ton  of  iron  as  the  cupola  does. 

A  little  limestone,  equal  to  about  1  per  cent  of  the  iron,  is 
added  as  a  flux.     Its  purpose  is  practically  the  same  here  as  in 


TAPPING  HOLE 


FIG.  83. — Section    of    typical    cupola. 

the  reduction  of  the  iron  ores;  namely,  to  combine  with  the 
gangue  in  the  pig  iron  and  the  ash  of  the  fuel  and  to  produce  a 
fusible  slag  which  will  float  on  the  surface  of  the  molten  iron. 

236.  The  Cupola. — The  cupola,  which  is  generally  used  for 
remelting  the  pig  and  scrap  iron,  is  somewhat  like  a  small  blast 
furnace.  It  consists  of  a  steel  shell  lined  with  firebrick  and 
provided  with  a  row  or  two  of  tuyeres  near  the  base,  through 


180 


MATERIALS  OF  CONSTRUCTION 


which  the  air  blast  enters  at  a  pressure  of  about  1  Ib.  per 
square  inch.  The  hearth,  with  a  cinder  notch  for  slag  and  a  tap 
hole  for  the  molten  iron,  is  at  the  bottom  of  the  furnace.  The 
charging  door  is  located  on  the  side  and  a  little  more  than  halfway 


FIG.  84. — Zones  in  cupola.     (Stoughton.) 

toward  the  top  of  the  stack.  The  stack  is  open  at  the  top  to  allow 
the  escape  of  the  burned  gases. 

A  cupola  may  be  divided  into  four  zones:  (1)  The  bottom  part 
or  hearth  which  contains  the  molten  iron  and  slag;  (2)  the  tuyere 
or  combustion  zone  where  the  air  blast  enters  the  furnace  and 
the  greatest  heat  is  developed;  (3)  the  melting  zone,  which  is 
located  just  above  the  combustion  zone,  where  the  iron  starts 
to  melt;  and  (4)  the  stack  zone  which  extends  from  the  melting 
zone  to  the  charging  door. 

The  operation  of  the  cupola  is  practically  the  same  as  that  of 
a  small  blast  furnace,  except  that  there  is  very  little  deoxidation, 
the  amount  of  fuel  used  is  less,  the  pressure  of  the  air  blast  is 
less,  and  no  use  is  made  of  the  escaping  gases.  About  100 
cu.  ft.  of  air  is  required  per  pound  of  coke.  The  cupola  is 
operated  almost  continually.  It  is  used  for  making  practically 
all  of  the  gray  cast  iron. 


CAST  IRON  181 

237.  The  Air  Furnace. — The  air  furnace  consists  essentially 
of  a  hearth  with  a  sloping  roof,  a  grate  or  firebox  at  one  end,  and 
a  stack  with  suitable  flue  and  draft  arrangements  at  the  other 
end.  The  walls  of  the  furnace  are  of  heavy  brick  masonry 
reinforced  with  cast-iron  plates  fastened  together  with  wrought- 
iron  bolts.  The  hearth  bottom  is  a  mixture  of  sand  and  fireclay. 
Openings  are  provided  for  charging  the  furnace  and  for  removing 


FIG.  85. — Longitudinal  section  of  an  air  furnace. 

the  slag  and  molten  iron.  This  furnace  is  somewhat  like  the 
furnace  used  in  the  wet  puddling  process  of  making  wrought  iron. 

The  air  furnace  is  used  for  .making  white  cast  iron,  malleable 
castings,  and  special  cast  irons  of  particular  compositions. 

In  operating  the  air  furnace,  the  fire  is  first  started  and  the 
furnace  heated,  and  then  the  pig  iron,  scrap  iron,  flux,  etc.  are 
placed  on  the  hearth.  The  temperature  is  controlled  by  dampers 
in  the  firebox  and  stack.  The  furnace  man  rabbles  the  bath  and 
skims  off  the  slag  from  time  to  time.  The  length  of  time  required 
is  greater  than  in  the  case  of  the  cupola. 

C.  FOUNDRY  WORK 

238.  Definition   of   Founding. — Founding   is   the   process   of 
making  iron  castings  by  pouring  the  molten  iron  into  molds  of 
the   desired   shape   and   size   which   the   metal   assumes   upon 
becoming  cold. 

In  founding,  the  following  things  are  important: 

1.  The  selection  and  preparation  of  the  iron  used  so  that  it  will 
have  the  correct  proportions  of  certain  chemical  elements  required 
to  make  good  castings. 

2.  Patterns  and  cores  which  are  properly  designed  and  made. 

3.  The  selection  of  the  proper  materials  for,  and  the  prepara- 
tion of,  the  hollow  molds  which  receive  the  molten  metal. 

239.  Patterns  and  Cores. — The  patterns  are  usually  made  of 
a  thoroughly  seasoned  wood,   white   pine   or  mahogany,   and 


182  MATERIALS  OF  CONSTRUCTION 

shellacked  to  keep  the  wood  from  being  affected  by  moisture. 
Sometimes  they  are  made  of  metal  or  plaster  of  Paris. 

Patterns  must  be  made  so  that  they  can  be  removed  from  the 
mold.  They  should  have  no  sharp  corners  as  these  cause  internal 
stresses  when  the  casting  shrinks  in  cooling.  Fillets  may  be 
placed  in  sharp  corners  to  round  them.  As  cast  iron  shrinks  in 
cooling,  the  patterns  must  be  made  a  little  larger  to  allow  for 
this  shrinkage.  Pure  iron  will  shrink  J^o  in.  for  each  foot  in 
length,  while  impure  iron  will  shrink  to  a  lesser  extent,  depending 
upon  the  amount  and  kind  of  impurities  present.  The  allowance 
made  for  shrinkage  varies  from  ^2  in.  per  foot  in  large  and  bulky 
castings  to  %  in.  per  foot  for  bars.  Often  the  patterns  are  made 
to  come  apart  in  two  or  more  places  so  as  to  aid  in  making  the 
molds.  The  surfaces  of  patterns  should  be  tapered  so  that  they 
can  be  easily  withdrawn  from  the  mold.  The  making  of  the 
patterns  is  of  great  importance  in  foundry  work  and  should  be 
done  only  by  workmen  skilled  in  this  work. 

The  cores,  which  are  used  to  form  the  hollow  spaces  in  the 
castings,  are  made  of  damp  sand  or  clay  for  small  molds  and  are 
constructed  of  built-up  brickwork  plastered  with  loam  for  the 
large  castings,  such  as  for  large  water  pipes,  etc, 

240.  Molds. — Molding  sand  consists  mostly  of  silica,  from 
90  to  95  per  cent,  which  makes  the  sand  refractory;  from  4  to  8 
per  cent  of  alumina  and  magnesia  which  furnish  cohesion  and 
plasticity;  about  1.5  per  cent  or  less  of  iron  oxide ;  and  about  0.5  per 
cent  of  lime.  Very  little  iron  oxide  and  lime  are  desirable  as 
they  make  the  sand  less  refractory.  Sand  that  is  very  fine 
compacts  too  much,  thus  preventing  the  gases  from  escaping. 
This  confined  gas  causes  the  formation  of  blow  holes.  Coarse 
sand  lacks  cohesion  and  makes  inferior  castings. 

Green  sand  molds  are  the  most  commonly  used  molds.  They 
are  made  of  molding  sand  which  is  first  uniformly  dampened 
and  then  lightly  rammed  around  the  pattern  to  obtain  the 
desired  shape.  The  molds  are  usually  made  in  open  frames  of 
iron  or  wood  called  core  boxes  or  flasks.  The  core  boxes  often 
consist  of  two  or  more  parts  for  convenience  in  molding.  Besides 
the  space  for  the  casting,  there  must  be  an  opening  leading 
from  the  outside  of  the  mold  to  the  casting  space  to  permit  of  the 
pouring  of  the  molten  iron.  There  should  also  be  a  skimmer  to 
remove  the  slag,  and  a  dirt  riser  between  the  pouring  gate  and 


CAST  IRON 


183 


the  casting.  At  the  other  end  of  the  casting,  there  should  be  a 
feeding  gate.  These  openings  are  usually  made  by  inserting 
plugs  in  the  sand  when  the  mold  is  made,  and  then  removing  the 
plugs  when  it  is  time  to  pour  the  iron.  Small  vent  holes  must  be 
made  in  the  mold  to  allow  of  the  escape  of  the  gases  when  the  iron 
is  poured. 

For  dry  sand  molds  a  loamy  sand  is  used  which  is  first  roughly 
molded  into  shape  and  then  dried  in  an  oven  and  finished  with  a 


5  1 

I 

i2 

'•— 

X. 

1 

%&\ 

lifl® 

.';  ;:V 

M 

•fe^- 

1 

fcirffl 

n< 

.—.:i 

i 

o; 

^ 

IN 

Costing 

m 

S— 

:r?.V 

->•:'••--'•: 

'£';•'&•', 

FIG.  86. — Section   of   a   green   sand   mold. 

tool.  These  molds  give  better  castings  than  the  green  sand 
molds  do  and  they  require  no  patterns,  but  they  are  more 
expensive. 

Loam  molds  are  generally  used  for  large  castings.  These 
molds  are  built  up  of  brickwork,  and  the  surfaces  are  finished 
by  plastering  with  loam.  The  whole  must  be  thoroughly 
dried  before  using.  Loam  molds  are  the  most  expensive 
molds. 

Chills  are  metal  molds  used  for  certain  castings,  or  are  simply 
pieces  of  metal  placed  in  other  molds.  This  metal  causes  the 
molten  iron  that  comes  in  contact  with  it  to  chill,  or  cool  rapidly, 
and  form  a  hard  surface.  In  order  to  prevent  an  explosion, 
when  the  hot  metal  comes  in  contact  with  the  cold,  it  is  necessary 
to  heat  the  chills  to  a  temperature  of  about  350  degrees  Fahren- 
heit before  pouring  the  iron.  These  molds  are  used  in  making 
cast  car  wheels,  chilled  rolls,  etc. 

241.  Pouring  and  Cleaning  the  Castings. — When  the  mold  is 
ready,  molten  pig  iron  is  drawn  from  the  cupola  into  a  ladle  and 
conveyed  to  the  mold.  The  molder  holds  the  ladle  as  close  as 
he  can  to  the  pouring  gate  and  then  pours  the  molten  iron  into 
the  mold.  If  it  is  a  top  pouring  ladle,  a  bar  is  used  to  keep  back 
the  slag.  The  molder  stops  pouring  when  the  metal  appears  at 


184  MATERIALS  OF  CONSTRUCTION 

the  top  of  the  riser.  Each  mold  must  be  filled  in  one  operation, 
or  planes  of  separation  will  be  formed  in  the  casting.  When  the 
castings  have  become  solid,  they  are  removed  from  the  molds 
and  allowed  to  cool. 

After  the  castings  have  cooled,  they  usually  have  to  be  cleaned 
of  the  sand  that  sticks  to  them.  For  small  castings,  a  common 
method  of  cleaning  is  to  place  them  in  a  tumbling  barrel  with 
some  pieces  of  very  hard  iron.  The  barrel  is  rotated  slowly  and 
the  tumbling  about  of  the  castings  knocks  the  sand  and  scale 
off  of  their  surfaces. 

A  better  method  of  cleaning  is  to  pickle  the  castings  by  immers- 
ing them  in  a  dilute  solution  of  sulphuric  or  muriatic  acid. 
The  time  required  is  about  12  hours  in  a  15  per  cent  solution. 
When  the  castings  are  removed  from  the  pickling  solution,  they 
must  be  carefully  washed  in  water  to  remove  all  traces  of  the  acid. 

The  sand  blast  is  a  very  convenient  way  of  cleaning  the  cast- 
ings, especially  those  which  are  large  or  which  have  irregular 
surfaces. 

The  irregularities  left  by  breaking  off  the  gates,  risers,  etc. 
may  be  removed  with  a  file,  an  emery  wheel,  or  a  cold  chisel 
and  hammer.  Sometimes  a  pneumatic  chipping  tool  can  be 
economically  used. 

242.  Defects   in   Castings. — The   most    common    defects   in 
castings  are: 

1.  Blow  Holes. — These  are  caused  by  the  formation  of  steam 
when  the  hot  metal  comes  in  contact  with  the  damp  sand  of  the 
molds. 

2.  Sand  Holes  and  Rough  Surfaces. — These  are  caused  by  the 
failure  or  breaking  down  of  the  molds  in  places. 

3.  Cracks. — These  are  caused  by  unequal  shrinkage  in  different 
parts  of  the  casting  when  it  cools. 

4.  Cold  Shorts  or  Seams. — These  are  caused  by  cooling  the 
iron  so  quickly  that  it  does  not  completely  fill  the  molds. 

D.  CONSTITUTION  AND  COMPOSITION  OF  CAST  IRON 

243.  Constitution  and  Composition  of  Cast  Iron  in  General. — 

Cast  iron  usually  contains  from  90  to  96  per  cent  of  iron;  2J^  to 
4^2  per  cent  of  carbon;  0.5  to  4.0  per  cent  of  silicon;  and  small 
percentages  of  manganese,  phosphorus,  sulphur,  and  other  chem- 
ical elements. 


CAST  IRON  185 

The  most  important  element  in  cast  iron,  besides  the  iron,  is 
carbon.  It  may  be  present  as  free  carbon  (graphite)  or  as 
combined  carbon.  Carbon  combines  with  iron  and  forms 
cementite,  Fe3C.  This  cementite  may  combine  with  free  iron 
(ferrite)  and  form  pearlite,  which  consists  of  about  6  parts 
of  ferrite  to  1  of  cementite.  Thus  a  cast  iron  may  be  composed 
of  ferrite,  graphite,  cementite,  and  pearlite. 

Ferrite,  or  free  iron,  is  soft,  weak,  and  tough.  Graphite  is 
weak.  Cementite  contains  6.67  per  cent  of  carbon  combined 
with  iron,  that  is,  1  part  of  carbon  and  15  parts  of  iron.  It  has 
great  strength,  is  very  brittle,  and  is  harder  than  the  hardest  steel. 
Pearlite  is  more  ductile,  less  hard  and  less  strong  than  cementite, 
but  is  stronger  and  harder  than  ferrite. 

If  a  section  of  ordinary  cast  iron  is  examined  under  the  micro- 
scope, flakes  of  graphite  will  be  found  enmeshed  in  a  matrix 
composed  of  ferrite,  cementite,  or  pearlite,  or  combinations  of 
these.  The  proportions  of  the  four  materials  vary  considerably 
in  different  cast  irons,  some  cast  irons  containing  practically  no 
free  carbon  and  others  containing  practically  no  combined 
carbon. 

When  the  cast  iron  is  in  a  molten  state,  the  carbon  is  in  solution 
with  the  iron.  Silicon  and  aluminum  tend  to  decrease  the 
amount  of  carbon  that  can  be  held  in  solution,  while  manganese 
and  chromium  increase  the  solubility. 

Slow  cooling  in  the  solidifying  of  cast  iron  allows  the  carbon  to 
separate  out  and  appear  in  the  form  of  flakes  (graphite).  The 
presence  of  aluminum  and  silicon  aid  in  this  separation  of  the 
carbon  and  iron  during  the  solidifying.  Slow  cooling  tends  to 
produce  what  is  known  as  gray  cast  iron. 

If  cast  iron  is  cooled  rapidly  from  the  molten  state,  the  carbon 
tends  to  stay  combined  with  the  iron  (because  it  does  not  have 
time  to  separate  out)  and  produce  what  is  known  as  white  cast 
iron.  Chromium  and  manganese,  when  present,  help  to  keep 
the  carbon  in  the  combined  form. 

244c  Effect  of  Carbon  in  Cast  Iron. — Carbon  has  more  effect 
on  the  properties  of  cast  iron  than  any  other  element  present, 
excepting  the  iron  itself.  Carbon  usually  varies  in  amount  from 
3  to  4  per  cent.  The  properties  of  cast  iron  depend  to  a  large 
extent  on  the  amount  of  carbon  present  and  also  on  the  form 
that  it  is  in,  i.e.,  combined  or  free. 

Cast  iron  is  usually  classified  according  to  the  different  form  in 


186  MATERIALS  OF  CONSTRUCTION 

which  the  carbon  occurs.  There  are  three  different  classes  as 
follows : 

1.  White  Cast  Iron — where  the  carbon  is  combined  with  the 
iron. 

2.  Gray  Cast  Iron — where  the  carbon  has  separated  from  the 
iron  and  is  present  in  the  form  of  graphite. 

3.  Mottled  Cast  Iron — a  mixture  of  gray  and  white  cast  iron. 
The  amount  of  combined  carbon  has  a  great  influence  on  the 

properties  of  cast  iron.  This  influence  may  be  summarized 
briefly  as  follows: 

As  the  ratio  of  combined  carbon  to  total  carbon  increases  from 
zero  to  one:  The  name  of  the  matrix  changes  from  low-carbon 
steel  to  medium  carbon  steel,  then  to  high-carbon  steel,  and  then 
to  white  cast  iron. 

The  name  of  the  cast  iron  as  a  whole  changes  from  open  gray  or 
very  graphitic  cast  iron  to  close  gray  cast  iron,  then  to  mottled 
cast  iron,  and  then  to  white  cast  iron.  The  percentage  of  ferrite 
decreases  while  the  percentage  of  cementite  increases. 

The  strength  increases  for  a  while  (until  the  percentage  of 
combined  carbon  is  about  1.2  per  cent)  and  then  decreases. 

The  hardness  and  brittleness  increase,  while  the  ductility 
decreases. 

The  ability  to  resist  shock  (toughness)  decreases  rapidly. 

The  ease  of  machining  decreases. 

White  cast  iron  consists  essentially  of  cementite  and  pearlite 
and  is  harder  and  more  brittle  than  gray  cast  iron. 

In  gray  cast  iron,  the  amount  of  graphite  varies  from  2  to  4 
per  cent,  while  the  amount  of  the  combined  carbon  is  less  than 
1^2  Per  cent.  Gray  cast  iron  is  composed  of  a  mixture  of  ferrite, 
graphite,  and  cementite.  This  iron  is  softer,  tougher,  weaker, 
and  less  brittle  than  white  cast  iron. 

Mottled  cast  iron  is  a  mixture  of  particles  of  white  and  gray 
cast  irons  and  contains  ferrite,  graphite,  cementite,  and  pearlite 
in  various  proportions.  Its  properties  depend  upon  the  relative 
amounts  of  gray  and  white  cast  iron. 

245.  Effect  of  Silicon,  Sulphur,  Phosphorus,  and  Manganese 
on  Cast  Iron. — Ordinary  cast  iron  contains,  besides  iron  and 
carbon,  four  other  chemical  elements  that  are  of  importance, 
namely  silicon,  sulphur,  phosphorus,  and  manganese.  Cast  iron 
also  often  contains  very  small  percentages  of  other  chemical 
elements  such  as  aluminum,  oxygen,  nitrogen,  copper,  nickel, 


CAST  IRON  187 

tin,  chromium,  etc.  These  latter  elements  are  not  present  in 
large  enough  quantities  in  ordinary  cast  iron  to  cause  any 
noticeable  effect  upon  its  properties. 

Silicon. — The  amount  of  this  element  present  usually  varies 
from  0.5  to  4.0  per  cent,  and  it  aids  in  determining  the  suitability 
of  the  iron  for  various  purposes.  A  little  silicon,  from  0.8  to 
1.8  per  cent,  makes  the  iron  soft  and  tough  and  gives  the  best 
strength  results.  More  or  less  silicon  tends  to  make  the  iron 
brittle  and  hard.  About  3  per  cent  makes  the  carbon  separate 
out  in  flake  form  (graphite).  Silicon  aids  in  foundry  work  by 
tending  to  increase  the  fluidity,  eliminate  the  blow  holes,  and 
decrease  the  shrinkage  when  properly  used.  It  reduces  the  chill 
in  casting. 

Sulphur. — This  element  helps  to  keep  the  carbon  in  the  com- 
bined form  and  tends  to  make  the  iron  hard,  brittle,  and  weak. 
It  also  causes  "red  shortness;"  i.e.,  makes  the  iron  very  brittle 
at  a  red  heat.  Such  iron  is  not  good  for  steel  manufacture.  In 
foundry  work,  sulphur  reduces  the  fluidity  and  increases  the  chill. 
Good  cast  iron  rarely  contains  more  than  0.15  per  cent  of  sulphur. 

Phosphorus. — The  fusibility  and  fluidity  of  the  iron  are 
increased  by  from  2  to  5  per  cent  of  phosphorus,  thus  helping  in 
the  making  of  fine  castings  in  the  molds.  From  1.0  to  1.5  per  cent 
of  phosphorus  is  often  used  for  fluidity  and  softness,  but  more 
than  1.5  per  cent  tends  to  make  the  iron  brittle  and  hard. 
For  the  best  strength  results,  not  over  0.55  per  cent  of  phos- 
phorus should  be  present.  Phosphorus  tends  to  reduce  the 
shrinkage  and  chill  in  castings.  If  the  iron  is  to  be  used  for 
steel  making  by  the  acid  bessemer  or  open-hearth  processes,  the 
phosphorus  content  should  be  less  than  0.07  per  cent. 

Manganese. — The  amount  of  this  element  present  may  vary 
from  0  to  80  per  cent,  but  rarely  exceeds  2  per  cent  in  ordinary 
castings.  Iron  that  is  to  be  used  for  steel  making  should  have 
some  manganese  present,  as  the  manganese  tends  to  prevent 
the  absorption  of  sulphur  in  remelting  and  also  helps  to  neutralize 
the  silicon  besides  making  the  steel  more  workable.  Less 
than  1.0  per  cent  of  manganese  has  practically  no  effect  on 
the  iron,  while  about  1.5  per  cent  makes  the  iron  fine  grained 
and  hard  to  tool.  Foundry  iron  usually  contains  less  than  1.0 
per  cent  of  manganese.  Manganese  increases  the  shrinkage, 
decreases  the  magnetism,  and  increases  the  solubility  of  carbon 
in  iron.  Speigeleisen  is  iron  containing  from  10  to  50  per  cent 


188  MATERIALS  OF  CONSTRUCTION 

of  manganese.  It  is  capable  of  taking  a  high  polish  and  is  very 
hard,  resisting  cutting  by  hard  cast  steel  tools.  If  the  iron 
contains  more  than  50  per  cent  of  manganese,  it  is  called 
ferromanganese. 

246.  Effect  of  Some  Other  Chemical  Elements  on  Cast  Iron.— 
Many  other  elements  are  often  found  to  some  extent  in  cast  iron 
in  very  small  quantities,  and  these  elements  may  have  some  effect 
on  the  properties  of  the  iron. 

Copper. — From  0.1  to  1.0  per  cent  closes  the  grain  of  cast 
iron,  but  does  not  appreciably  cause  brittleness.  It  makes  the 
iron  unsuitable  for  making  malleable  iron. 

Aluminum. — From  0.2  to  1.0  per  cent  (added  to  the  ladle  in  the 
form  of  a  FeAl  alloy)  increases  the  softness  and  strength  of  white 
iron;  added  to  gray  iron,  it  softens  and  weakens  it.  About  0.1  per 
cent  of  aluminum  has  the  same  effect  as  1.5  per  cent  of  silicon. 
Aluminum  is  undesirable. 

Tin. — Increases  hardness  and  fusibility  and  decreases  mallea- 
bility besides  making  the  iron  unfit  for  conversion  into  malleable 
cast  iron. 

Vanadium. — Very  small  quantities  increase  softness  and 
ductility.  As  much  as  0.15  per  cent  added  to  the  ladle  in  the 
form  of  a  ground  FeVa  alloy  greatly  increases  the  strength  of 
cast  iron.  Vanadium  also  acts  as  a  deoxidizer  and  as  an  alloying 
material. 

Titanium. — Increases  the  strength,  when  added  in  small 
amounts,  such  as  a  2  per  cent  or  a  3  per  cent  TiFe  alloy 
containing  about  10  per  cent  of  titanium. 

E.  PHYSICAL    AND    MECHANICAL    PROPERTIES    AND    USES    OF 

CAST  IRON 

247.  Strength  of  Cast  Iron  in  General. — In  general,   large 
castings  are  not  so  strong  as  small  ones.     The  shape  of  a  casting 
also  affects  the  strength;  sharp  reentering  angles  cause  planes  of 
weakness  in  cooling,  while  curved  surfaces  are  not  so  weakened. 
The   design   of   the   castings   is   of  importance.     The   methods 
of  founding  also  greatly  influence  the  strength.     For  example,  if  a 
hollow  column  is  cast  in  a  horizontal  position,  the  slag    and 
foreign  materials  will  tend  to  collect  on  the  upper  side  and  weaken 
that  part  of  the  column.     Casting  the  column  in  a  vertical 
position  will  cause  the  strength  of  all  sides  to  be  the  same.     As 


CAST  IRON 


189 


noted  in  previous  articles,  the  presence  of  different  chemicals, 
especially  carbon  and  its  combinations,  have  a  great  influence  on 
the  strength  and  properties  of  cast  iron. 

248.  Tensile  Strength  of  Cast  Iron. — The  combined  carbon 
(for  a  total  carbon  content  of  about  4  per  cent)  in  cast  iron  should 
be  between  0.6  and  1.2  per  cent  to  obtain  the  maximum  tensile 
strength. 

The  tensile  strength  of  cast  iron  varies  from  10,000  to  45,000  Ib. 
per  square  inch,  but  for  ordinary  castings  it  may  be  taken 


.001  .002  .003  .004 

.Strain,  Inches   per  Inch 
FIG.  87. — Stress-strain  diagrams  for  cast  irons  in  tension. 


between  15,000  and  30,000  Ib.  per  square  inch.  The  minimum 
specification  requirements  for  gray  iron  castings  are:  18,000  Ib. 
per  square  inch  for  lightweight  castings;  21,000  Ib.  per  square 
inch  for  medium  castings;  and  24,000  Ib.  per  square  inch  for 
heavy  castings. 

The  stress-strain  diagram  for  tension  is  a  curved  line  which 
shows  no  well-defined  elastic  limit;  but,  if  the  elastic  limit  is 
considered  as  the  unit  stress  at  which  permanent  set  takes  place, 
cast  iron  may  be  said  to  have  an  elastic  limit  which  varies  from 
30  to  60  per  cent  of  the  ultimate,  according  to  the  grade  of  the 
iron. 

The  modulus  of  elasticity  in  tension  is  a  variable  quantity, 
depending  upon  the  kind  of  iron  and  the  unit  stress  at  which  it  is 
computed.  It  will  average  about  14,000,000  Ib.  per  square  inch 
with  probable  variations  of  25  per  cent  or  more. 


190 


MATERIALS  OF  CONSTRUCTION 


The  percentage  of  elongation  is  very  small,  rarely  exceeding 
3  or  4  per  cent  for  any  grade  of  cast  iron. 

The  reduction  of  area  is  so  small  as  to  be  inappreciable. 

The  fracture  of  cast  iron  in  tension  is  square  across;  that  of  gray 
cast  iron  being  gray  in  color,  highly  crystalline  in  appearance,  and 
showing  flakes  of  free  graphite,  while  the  fracture  of  white  cast 


.  90,000 


.002    .OO4.0O6  .COO  .OIO    .OI2    .OK    .OI6    .016    .020    -O£2  .024 

Strain,  Inches  per  Inch 
FIG.  88. — Stress-strain  diagrams  for  cast  irons  in  compression. 

iron  has  a  white  metallic  color  and  a  finely  crystalline  appearance. 

249.  Compressive  Strength  of  Cast  Iron. — The  compressive 
strength  of  cast  iron  depends  upon  about  the  same  factors  as  the 
tensile  strength.  For  the  best  results,  the  percentage  of  com- 
bined carbon  should  be  a  little  more  than  that  for  tension,  say 
from  1.0  to  1.2  per  cent  for  a  total  carbon  content  of  about  4.0 
per  cent. 

In  compression,  the  strength  of  cast  iron  may  be  taken  from 
60,000  to  100,000  Ib.  per  square  inch,  though  tests  have  shown 
variations  from  45,000  to  200,000  Ib.  per  square  inch,  depending 
upon  the  kind  of  iron,  structure,  composition,  size,  etc. 

The  stress-strain  diagram  for  compression  shows  a  fairly  well 
defined  yield  point,  varying  from  35  to  60  per  cent  of  the  ultimate, 
depending  on  the  grade  of  the  iron. 

The  modulus  of  elasticity  in  compression  varies,  according  to 
the  kind  and  grade  of  the  iron  and  the  unit  stress  at  which  it  is 
computed,  from  10,000,000  to  25,000,000  Ib.  per  square  inch  with 
an  average  of  about  14,000,000  Ib.  per  square  inch. 

When  cast  iron  is  stressed  to  failure  in  compression,  the  failure 


CAST  IRON  191 

is  usually  shear  along  a  plane  making  approximately  55  degrees 
with  the  line  of  loading. 

250.  Transverse  Strength  of  Cast  Iron. — At  the  present  time 
the  cross-bending  strength  of  cast  iron  is  the  most  important 
criterion  of  its  quality,  the  tensile  strength  probably  ranking 
second.  The  transverse  strength  is  usually  expressed  by  the 
term  "modulus  of  rupture"  and  is  computed  by  the  formula 
S  =  Mv/I. 

An  average  value  of  the  transverse  strength  of  cast  iron  is  about 
35,000  or  40,000  Ib.  per  square  inch,  though  tests  have  shown  a 
variation  of  from  10,000  to  65,000  Ib.  per  square  inch,  depending 
on  the  grade  of  iron,  the  structure,  method  of  founding,  length  of 
span,  etc.  The  percentage  of  combined  carbon  for  the  greatest 
strength  should  be  between  the  values  for  the  highest  strength 
in  compression  and  tension. 

The  minimum  requirements  for  strength  in  transverse  tests  on 
the  " arbitration  test  bar"  over  a  12-in.  span  are  as  follows: 

CENTER   LOAD,    MODULUS  OP  RUPTURE, 
CASTING  POUNDS       POUNDS  PER  SQUARE  INCH 

Light  castings 2,500  39,000 

Medium  castings 2,900  45,000 

Heavy  castings 3,300  52,000 

The  deflection  at  the  center  shall  not  be  less  than  0.10  in. 

The  " arbitration  test  bar"  is  a  bar  15  in.  long  and  \Y±  in.  in 
diameter,  cast  vertically  in  a  green  sand  mold  that  is  cold  and 
thoroughly  dry  when  the  iron  is  poured.  Two  bars  should  be 
cast  from  each  heat. 

The  " modulus  of  shock  resistance"  of  cast  iron  is  equal  to  the 
product  of  one-half  the  center  load  and  the  deflection  divided  by 
the  volume  of  the  specimen  between  the  supports.  It  is  approxi- 
mately the  same  as  the  energy  of  rupture. 

The  failure  of  cast  iron  in  cross  bending  is  a  failure  by  tension 
on  the  tension  side  of  the  beam. 

The  modulus  of  elasticity  of  cast  iron  in  cross  bending  is  about 
the  same  as  that  in  tension  and  compression,  averaging  about 
14,000,000  Ib.  per  square  inch  with  large  variations  depending 
upon  the  grade  and  structure  of  the  iron,  etc. 

The  modulus  of  elasticity  in  cross  bending  may  be  considered  as 
a  measure  of  the  stiffness  of  the  cast  iron,  or  its  ability  to  resist 
transverse  loads  without  bending  much. 


192  MATERIALS  OF  CONSTRUCTION 

251.  Miscellaneous  Properties  of  Cast  Iron. — The  computed 
ultimate  resistance  to  shear  and  torsion  varies  from  20,000  to 
35,000  Ib.  per  square  inch  for  cast  iron. 

The  fusibility  of  cast  iron  depends  upon  the  percentage  of 
carbon  and  some  of  the  other  elements.  An  average  value  is 
2,500  degrees  Fahrenheit. 

The  coefficient  of  expansion  is  about  0.0000062  per  degree 
Fahrenheit. 

The  specific  gravity  of  cast  iron  varies  from  6.9  to  7.5.  It  is 
usually  taken  at  7.22,  corresponding  to  a  weight  of  450  Ib.  per 
cubic  foot.  In  general,  the  specific  gravity  increases  with  the 
strength  and  the  number  of  remeltings. 

The  shrinkage  of  cast  iron  in  cooling  varies  according  to  its 
shape  and  purity,  varying  from  J^2  m>  Per  foot  for  large  castings 
to  %  in.  per  foot  for  bars.  Pure  cast  iron  will  shrink  about  %Q 
in.  per  foot  of  length. 

When  dropped  on  a  concrete  or  stone  floor,  white  cast  iron  has 
a  bright  metallic  ring,  malleable  cast  iron  a  dull  ring,  and  gray 
cast  iron  a  "dead"  sound. 

252.  Allowable  Working  Stresses  for  Cast  Iron. — Allowable 
unit  working  stresses  for  cast  iron  depend  upon  the  character 
of  the  loads,  grade  of  metal,  and  size  of  casting.     Large  castings 
are  weaker  than  small  ones  due  to  shrinkage,  nonuniformity  of 
structure,  and  chance  for  defects. 

For  variable  loads,  the  allowable  working  stresses  in  tension 
are  3,000  Ib.  per  square  inch;  in  compression,  16,000  Ib.  per 
square  inch;  and  in  shear  about  2,500  Ib.  per  square  inch.  Work- 
ing stresses  for  steady  loads  may  be  taken  about  25  per  cent 
greater  than  those  for  variable  loads.  For  repetitive  loads, 
changing  alternately  from  tension  to  compression,  the  allowable 
unit  working  stress  should  not  be  over  1,000  Ib.  per  square  inch. 
Cast  iron  is  too  brittle  to  be  used  to  resist  shocks  or  impact 
loads. 

253.  Uses  of  Cast  Iron. — For  structural  purposes,  cast  iron  is 
not  used  to  so  large  an  extent  as  wrought  iron  and  steel.     Cast 
iron  can  be  used  for  posts,  columns,  column  bases  and  caps,  bear- 
ing plates,  etc. 

Cast  iron  is  much  used  for  parts  of  machines  because  it  is  cheap 
and  can  be  cast  in  almost  any  form.  In  places  where  cast  iron 
can  be  used,  it  suffers  but  little  from  competition  by  other 
metals. 


CAST  IRON  193 

F.  MALLEABLE  CAST  IRON 

254.  Definition  of  Malleable  Cast  Iron. — Malleable  cast  iron 
is  annealed  white  cast  iron  in  which  the  carbon  has  been  sep- 
arated from  the  iron  without  forming  flakes  of  graphite  as  in 
the  gray  cast  iron. 

255.  Making  the  Castings  for  Malleable  Cast  Iron. — White 
pig  iron,  containing  not  more  than  0.60  per  cent  of  manganese,  not 
more  than  0.22  per  cent  of  phosphorus,  and  not  more  than  0.05 
per  cent  of  sulphur,  is  used  in  the  manufacture  of  malleable  cast 
iron.     The  total  carbon  content  must  be  more  than  2.75  per  cent. 
The  amount  of  silicon  varies  inversely  with  the  size  of  the  casting; 
heavy  castings  require  about  1.0  per  cent,  and  light  castings 
about    2.0    per   cent  of  silicon.     Sometimes   malleable    scrap 
(never  over  20  per  cent),  steel  scrap  (never  over  10  per  cent),  or 
wrought-iron  scrap  (not  over  5  per  cent)  is  mixed  with  the  pig 
iron.     Malleable  scrap  is  hard  to  melt,    but  it    increases    the 
strength  of  the  castings.     Steel  scrap  and  wrought-iron  scrap 
tend  to  make  the  castings  stronger. 

The  white  pig  iron,  with  the  scrap,  is  melted  in  a  cupola,  an  air 
furnace,  or  an  open-hearth  furnace;  the  air  furnace  being 
generally  used.  The  molds  are  usually  green  sand  molds.  The 
molten  white  iron  must  be  poured  while  it  is  very  hot,  and  the 
pouring  must  be  done  very  rapidly  in  order  to  secure  good  cast- 
ings. After  cooling,  the  castings  are  cleaned  by  any  ordinary 
foundry  method,  and  the  imperfect  ones  rejected. 

256.  Annealing  the  Castings  for  Malleable  Cast  Iron. — The 
castings,  which  are  to  be  annealed,  are  placed  in  annealing  pots 
in  such  a  way  that  they  will  not  be  deformed  by  any  slight  settle- 
ments.    The  annealing  pots  are  made  of  cast  iron,  and  are  about 
18  by  24  in.  in  cross  section  and  from  15  to  48  in.  high. 

Iron  scale,  Fe2O3,  is  packed  in  the  pots  and  around  the  castings. 
Sometimes  the  slag  squeezed  from  wrought-iron  puddle  balls, 
powdered  hematite  ore,  or  magnetite  is  used  instead  of  the  iron 
scale.  This  iron  scale  acts  as  a  decarburizer.  Excess  space  in 
the  annealing  pots  may  be  filled  with  good  clean  silica  sand. 

The  annealing  pots  are  placed  in  an  oven  and  the  temperature 
raised  to  a  cherry  red  heat,  about  1,450  degrees  Fahrenheit,  and 
held  there  from  3  to  5  days,  depending  on  the  size  of  the  castings 
and  the  amount  of  decarburizing  desired.  Then  the  furnace  is 
allowed  to  cool  slowly  for  a  few  days  before  the  castings  are 
removed  and  cleaned. 

13 


194  MATERIALS  OF  CONSTRUCTION 

To  test  the  quality  of  the  annealing,  test  plugs  or  small  pro- 
jections about  ;Hj  by  %  in.  by  1  in.  long  are  cast  on  the  more 
important  pieces.  These  are  broken  off  and  the  fracture  exam- 
ined. If  properly  annealed,  the  interior  of  the  fracture  should 
have  a  black  velvety  surface  surrounded  by  a  band  of  dark  gray 
about  He  m-  thick.  This  dark  gray  band  should  in  turn  be 
surrounded  by  a  thin  white  band  about  ^4  in.  thick. 

The  effect  of  the  annealing  process  is  to  change  nearly  all  of  the 
carbon  from  the  combined  form  to  a  free  amorphous  form  called 
" temper"  carbon,  to  make  the  castings  " malleable,"  and  to 
about  double  their  tensile  strength.  The  decarburizer  (packing 
of  iron  scale)  prevents  the  oxidation  and  warping  of  the  castings, 
and  also  extracts  a  large  part  of  the  carbon  from  the  surfaces  of 
the  castings  to  a  depth  varying  from  He  to  Y%  in. 

257.  Properties    of    Malleable    Cast    Iron.     Structure. — The 
outermost  skin,  which  is  white  in  color  and  about  %4  in.  thick, 
consists  of  ferrite  with  a  few  impurities.     The  dark-gray  layer, 
from  %  to  J/f  e  m-  thick,  consists  of  ferrite  with  a  few  scattered 
particles  of  temper  carbon.     This  layer  is  much  stronger  and 
more  ductile  than  the  inner  portion.     The  black  interior  consists 
of  ferrite  and  many  particles  of  temper  carbon. 

The  tensile  strength  is  the  best  criterion  of  the  quality  of 
malleable  cast  iron.  Its  tensile  strength  is  about  45,000  Ib.  per 
square  inch,  with  a  yield  point  at  about  70  per  cent  of  the  ulti- 
mate. The  percentage  of  elongation  varies  from  2  to  7  per  cent 
over  a  gage  length  of  2  in. 

The  compressive  strength  of  small  prisms  of  good  malleable 
iron  (load  applied  parallel  to  skin)  will  vary  from  100,000 
to  150,000  Ib.  per  sq.  in. 

The  average  transverse  strength  (modulus  of  rupture)  is  about 
60,000  Ib.  per  square  inch.  Tests  have  given  results  varying 
from  54,000  to  90,000  Ib.  per  square  inch  for  a  1  in.  square  bar 
over  a  span  of  12  in.  The  deflection  varied  from  J/£  to  1%  in. 

Malleable  cast  iron  is  quite  tough,  and  is  much  more  able  to 
withstand  shocks  and  blows  than  the  cast  iron  from  which  it  is 
made. 

Malleable  castings  can  be  bent  when  cold,  and  can  be  forged 
and  welded  to  a  greater  or  less  extent. 

258.  Uses  of  Malleable  Cast  Iron. — Malleable  cast  iron  has 
no  structural  uses,  but  it  is  used  very  much  in  the  manufacture 
of  articles  which  are  too  complicated  in  form  to  be  readily  forged, 


CAST  IRON  195 

and  which  must  be  tougher  and  stronger  than  gray  cast  iron. 
Malleable  cast  iron  has  all  of  the  advantages  of  gray  cast  iron, 
with  respect  to  casting  in  various  shapes,  plus  toughness,  ductil- 
ity, and  strength  nearly  equal  to  that  of  some  steels.  Only  cast 
or  forged  steel  can  compete  with  malleable  cast  iron  in  many  of  its 
uses,  and  then  the  malleable  cast  iron  is  usually  cheaper. 

Malleable  cast  iron  is  used  in  the  manufacture  of  machinery 
parts,  pipe  fittings,  small  pinions,  parts  of  railway  rolling  stock 
such  as  journal  boxes,  brake  fittings,  etc.,  and  for  various  kinds 
of  hardware,  etc. 


CHAPTER  XII 
WROUGHT  IRON 

A.  DEFINITION  AND  CLASSIFICATIONS 

259.  Definition   of   Wrought   Iron. — Wrought   iron   may   be 
defined  as  nearly  pure  iron  intermingled  with  more  or  less  slag. 
The  name  "wrought  iron"  is  applied  to  that  commercial  form 
of  iron  which  is  obtained  by  refining  pig  iron  at  a  temperature 
not  high  enough  to  keep  the  metal  in  a  molten  state  after  the 
oxidation  of  the  impurities,  but  just  high  enough  to  keep  the  iron 
in  a  pasty  condition. 

Wrought  iron  is  made  in  a  reverberatory  furnace.  It  is 
composed  principally  of  pure  iron  (ferrite)  and  slag  (iron  silicate) 
together  with  small  amounts  of  impurities. 

260.  Classifications  of  Wrought  Iron. — Wrought  iron  may  be 
classified  according  to  the  method  of  manufacture,  or  according 
to  its  use. 

According  to  Method  of  Manufacture 

1 .  Charcoal  Iron. — Made  by  using  charcoal  fuel  and  a  charcoal 
hearth.     The  purest  grades  of  wrought  iron  are  made  by  this 
method. 

2.  Puddled  Iron. — Made  by  the  ordinary  wet  puddling  process 
of  manufacture. 

3.  Busheled  Scrap.— Made  as  described  in  Article  266. 

According  to  Use 

1.  Staybolt    Iron. — Made    from    puddled    or    charcoal    iron. 
While  not  the  strongest,  it  is  the  toughest  and  most  ductile 
wrought  iron.     Good  for  forging  and  welding. 

2.  Engine-bolt  Iron. — Made  from  the  same  material  as  the 
staybolt  iron.     It  is  a  little  stronger  but  less  tough  and  ductile. 

3.  Refined  Bar  Iron. — Made  from  a  mixture  of  muck  bars  and 
iron  scrap.     Less  strong,  ductile,  tough,  and  forgeable  than  the 
engine-bolt  iron. 

4.  Wrought  Iron  Plate. — Class  A.     Made  from  puddled  iron. 
A  strong  hard  iron,  but  less  ductile  and  tough  than  the  best 
grades  of  wrought  iron. 

197 


198  MATERIALS  OF  CONSTRUCTION 

5.  Wrought  Iron  Plate. — Class  B.  Made  from  a  mixture  of 
puddled  iron  and  scrap.  Not  so  good  as  the  class  A  plate. 
Neither  class  A  nor  class  B  plate  should  be  used  for  forging  or 
welding. 

B.  MANUFACTURE  OF  WROUGHT  IRON 

261.  The  Materials  for  the  Wet-puddling  Process. — Practi- 
cally all  of  the  wrought  iron  manufactured  at  the  present  time 
is  made  from  pig  iron  and  various  kinds  of  scrap  by  the  puddling 
process.     There    are    two    kinds    of    puddling    processes — wet 
puddling  and  dry  puddling.     The  latter  process  is  rarely  used. 

The  pig  iron  commonly  used  in  the  manufacture  of  wrought 
iron  is  forge  pig.  This  pig  iron  contains  from  1.0  to  1.5  per  cent 
of  silicon,  from  0.25  to  1.25  per  cent  of  manganese,  less  than 
1.00  per  cent  of  phosphorus,  and  less  than  0.10  per  cent  of  sul- 
phur. A  large  amount  of  silicon  is  desired  so  as  to  form  enough 
slag  to  cover  the  molten  iron.  The  amount  of  manganese  is 
not  important  as  it  is  practically  all  removed  in  the  manufacture. 
The  phosphorus  arid  sulphur  must  be  kept  low  as  they  are  not 
completely  removed. 

The  " fettling"  is  composed  of  the  strong  basic  iron  oxides  that 
are  used  to  line  the  furnace  hearth.  Some  of  these  fettling 
materials  are — basic  slag  from  the  puddling  furnace  or  reheating 
furnace,  hammer  slag  or  scale  from  a  rolling  mill,  and  hematite 
ore.  Enough  fettling  is  used  to  cover  the  hearth  to  a  depth  of 
about  5  in. 

The  fuel  used  is  a  bituminous  coal  that  burns  with  a  long 
flame. 

262.  The  Furnace  Used  in  the  Wet-puddling  Process.— The 
furnace  is  of  the  reverberatory  type  and  consists  essentially  of  a 
puddling  or  working  chamber  (hearth),  a  grate  or  firebox  at  one 
end,  and  a  stack  at  the  other  end.     The  furnace  is  made  of 
masonry  lined  with  firebrick.     The  outside  is  made  of  cast-iron 
plates  fastened  together  with  wrought-iron  bolts.     Iron  castings 
support  the  hearth  at  some  distance  above  the  floor  to  allow  for 
the  circulation  of  air  underneath.     The  hearth  has  a  sloping  roof 
which  deflects  the  flame  from  the  fire  down  upon  the  hearth. 
The  working  chamber  is  provided  with  openings  for  the  purpose 
of  charging  and  working  the  metal,  and  for  the  removal  of  the 
slag  and  the  puddled  iron.     The  fire  grate  has  about  one-third 


WROUGHT  IRON 


199 


of  the  area  of  the  hearth,  and  is  separated  from  the  hearth  by  a 
cast-iron  air-cooled  flue  covered  with  a  refractory  material. 
Sometimes  a  steam  jet  is  used  to  provide  more  air  for  the  fuel 
and  for  the  oxidation  of  the  impurities.  Dampers,  etc.  are 
provided  for  the  regulation  of  the  fire.  The  stack  is  connected 
with  the  hearth  by  suitable  flue  and  draft  openings,  and  is  also 
provided  with  dampers  to  aid  in  the  regulation  of  the  fire. 

263.  Operation  of  the  Furnace  Used  in  the  Wet-puddling 
Process. — -The  charge  of  the  furnace  consists  of  a  large  amount  of 
fettling,  which  is  uniformly  compacted  on  the  hearth,  and  about 


FIG.  89. — Section  of  a  puddling  furnace. 

500  lb.  of  gray  forge  iron  placed  on  top  of  the  fettling.  After  a 
melting  temperature  has  been  reached,  the  reduction  of  the 
impurities  occurs  in  four  different  stages: 

1.  The  " melting  down"  stage  lasts  about  half  an  hour  after 
the  fire  is  started,  by  the  end  of  which  time  the  iron  will  have 
melted  and  nearly  all  of  the  silicon  and  the  manganese  together 
with  part  of  the  phosphorus  and  a  little  of  the  sulphur  will  have 
been  oxidized.     These  oxides  leave  the  metal  and  join  the  slag. 

2.  The  " clearing"  stage  lasts  about  10  minutes,  and  in  this 
stage  the  remainder  of  the  silicon  and  of  the  manganese  is  oxidized 
together  with  a  further  quantity  of  phosphorus  and  sulphur. 
At  this  time  it  is  usually  necessary  to  add  more  red  oxide  of  iron 
to  make  the  slag  more  basic,  and  also  to  reduce  the  temperature 
of  the  furnace  somewhat  so  that  the  carbon  will  not  be  oxidized 
before  the  phosphorus  and  the  sulphur.     Vigorous  stirring  or 
"rabbling"  at  this  stage  tends  to  help  the  oxidation. 

3.  During  the  " boiling"  stage  practically  all  of  the  carbon  and 
most  of  the  remaining  phosphorus  and  sulphur  are  oxidized. 
The  iron  oxide  in  the  slag  unites  with  the  carbon  in  the  pig  iron, 
producing  carbonic  oxide  and  iron.     The  iron  combines  with  the 
iron  on  the  hearth,  while  the  carbonic  oxide  gas  rises  and  causes 


200 


MATERIALS  OF  CONSTRUCTION 


the  molten  metal  to  swell  up  and  boil.  When  this  gas  comes 
through  the  surface  of  the  bath,  it  burns  in  small  flames  of  a  light- 
blue  color.  The  slag  must  be  strongly  basic  in  order  to  keep  the 
phosphorus  and  sulphur  in  solution.  During  this  stage  the  slag 
sometimes  boils  over  the  edge  of  the  hearth  and  is  caught  and 
removed  by  means  of  a  slag  buggy.  The  puddler  vigorously 
stirs  or  rabbles  the  charge  to  prevent  the  iron  from  oxidizing,  to 
keep  it  from  settling  on  the  hearth,  and  also  to  secure  a  uniform 
product.  Finally,  the  iron  ceases  to  boil  and  " comes  to  nature7' 
forming  a  spongy  mass  of  metal  which  rests  on  the  bed  of  slag. 
4.  During  the  " balling"  stage,  which  occupies  about  20 
minutes,  the  temperature  of  the  furnace  is  lowered  and  the 


FIG.  90. — Showing  principle  of  a  merchant  bar  mill. 

pasty  mass  of  iron  is  divided  into  portions  small  enough  to  be 
removed  from  the  furnace  by  the  puddler.  Before  removing 
the  pasty  iron  from  the  furnace,  the  puddler  works  each  portion 
into  a  ball,  storing  the  balls  under  the  protection  of  the  fire 
bridge  to  prevent  the  oxidation  of  the  iron  before  the  balls  are 
taken  from  the  furnace.  Each  ball  weighs  about  100  Ib. 

264.  The  Dry-puddling  Process. — In  the  dry-puddling  process, 
white  pig  iron  is  charged  to  the  furnace  and  subjected  to  the 
action  of  an  oxidizing  flame.  In  this  process,  the  necessary 
oxygen  is  supplied  by  the  furnace  instead  of  by  the  fettling. 

285.  Mechanical  Treatment  of  the  Puddle  Balls. — Squeezing 
or  Shingling. — When  the  puddle  balls  are  removed  from  the 
furnace,  they  contain  much  slag.  This  slag  is  removed  to  a  large 
extent  by  squeezing  the  balls  in  a  squeezer,  which  reduces  the 
diameter  of  the  balls  about  one-half.  Sometimes  a  ball  is 
placed  under  a  steam  hammer  and  the  slag  pounded  or 
" shingled"  out.  The  squeezing  or  shingling  causes  a  rise  in 
the  temperature  of  the  ball  which  tends  to  melt  the  slag  and  thus 
aid  in  its  removal. 


WROUGHT  IRON  201 

Rolling  Muck  Bars. — After  the  squeezing,  the  balls  are  taken 
to  a  rolling  mill  and  rolled  and  cut  into  rectangular  bars  called 
"muck"  bars.  The  rolling  usually  removes  a  little  of  the 
remaining  slag. 

Reheating  and  Rerolling. — The  muck  bars  are  piled,  tied  in 
bundles  with  wire,  reheated  to  a  welding  heat,  and  rerolled  in 
commercial  shapes  (merchant  bars).  Sometimes  the  operations 
of  piling,  tying,  reheating,  and  rerolling  are  repeated  several 
times,  resulting  in  an  improvement  in  the  quality  and  an  increase 
in  the  strength  of  the  bars.  Not  much  advantage  is  gained 
by  reheating  and  rerolling  more  than  three  times.  The  shapes 
of  the  commercial  bars  are  sheets,  plates,  strips,  bars,  round  and 
square  rods,  angle  irons,  tee  irons,  channels,  I-beams,  Z-bars,  etc. 

266.  Wrought  Iron  Made  from  Scrap. — Sometimes  wrought- 
iron  scrap  is  tied  together,  heated,  and  rolled  into  commercial 
shapes.     Another  way  is  to  make  a  box  out  of  muck  bars,  fill  it 
with  scrap,  heat  it,  and  roll  it.     If  the  pieces  of  scrap  are  too 
small  or  too  irregular  to  be  tied  together  as  muck  bars  are,  they 
may  be  "busheled"  together,  placed  in  a  small  furnace,  and 
treated  as  an  ordinary  puddle  ball.     All  of  these  methods  of 
making  wrought  iron  from  scrap  result  in  an  inferior  product. 

If  some  steel  scrap  is  heated  with  the  muck  bars,  the  resulting 
product  will  have  many  of  the  properties  of  soft  steel. 

267.  Defects   in   Wrought   Iron. — The   principal   defects   in 
wrought  iron  are  rough  edges,  spilly  places,  blisters,  and  excess 
of  slag.     Rough  edges  are  due  to  careless  workmanship,  imper- 
fect rolls,  or  red  shortness.     Spilly  places  are  spongy  or  irregu- 
larly  spotted   parts,    and   are   generally   caused   by  imperfect 
puddling.     Blisters  are  caused  by  the  presence  of  gas,  probably 
carbonic  oxide,  in  the  iron  when  it  is  being  rolled.     An  excess 
of  slag  is  due  to  imperfect  or  insufficient  squeezing,  forging,  or 
rolling  of  the  balls  and  bars. 

C.  CONSTITUTION,  PROPERTIES,  AND  USES  OF  WROUGHT  IRON 

268.  Composition  and   Constitution   of   Wrought  Iron. — The 
following  table  gives  the  chemical  composition  of  some  kinds  of 
wrought  iron.     From  this  table  it  is  seen  that  wrought  iron  is 
nearly  all  pure  iron  with  a  little  slag.     The  strength  of  wrought 
iron  is  affected  to  some  extent  by  its  chemical  composition,  an 
increase  in  the  carbon  content  causing  an  increase  in  strength. 


202 


MATERIALS  OF  CONSTRUCTION 


CHEMICAL  COMPOSITION  OF  WROUGHT  IRON 


Chemical  element 

Common 
wrought  iron, 
per  cent 

Best 

wrought  iron, 
per  cent 

Swedish 
wrought  iron, 
per  cent 

Carbon 

0  05  to  0  10 

0  06 

0  050 

Phosphorus 

0  18  to  0  35 

0  15 

0  055 

Sulphur  

0  .  04  to  0  06 

0.03 

0.007 

Silicon  
Manganese  

0.20  to  0.23 
about  0  .  10 

0.20 
0.06 

0.015 
0.006 

Slag  

2  .  80  to  3  .  10 

2.80 

0.610 

Swedish  wrought  iron  is  a  very  pure  wrought  iron  made  in 
Sweden. 

The  constituents  of  wrought  iron  are  ferrite  (pure  iron),  slag 
(silicates  and  phosphates  of  iron  and  manganese),  and  a  little 
pearlite  due  to  the  presence  of  the  carbon.  The  little  carbon  in 
wrought  iron  combines  with  some  of  the  iron  to  form  cementite, 
which  in  turn  combines  with  ferrite  to  form  pearlite. 

The  size  of  the  crystalline  grains  of  ferrite  in  the  wrought  iron 
depends  on  the  temperature  from  which  the. hot  iron  is  cooled,  the 
length  of  time  held  at  that  temperature,  the  rate  of  cooling,  the 
mechanical  working  during  the  cooling,  and  the  temperature  at 
which  this  working  is  stopped.  High  temperatures  and  slow 
cooling  both  tend  to  increase  the  size  of  the  crystals.  Mechanical 
working  tends  to  overcome  the  bad  effects  of  coarse  crystals  by 
breaking  up  the  large  crystals  and  retarding  their  formation  and 
growth. 

269.  Tensile  Strength  of  Wrought  Iron.— The  tensile  strength 
of  wrought  iron  depends  upon  the  direction  of  the  load  in  regard 
to  the  grain  or  fibers  of  the  wrought  iron.  The  strength  across 
the  fibers  is  from  60  to  90  per  cent  of  the  strength  along  the  fibers. 

In  regard  to  the  effect  of  the  amount  of  reduction  in  size  due  to 
the  rolling,  tests  have  shown  that,  if  the  ratio  of  the  finished  size 
of  bar  to  the  size  of  pile  of  muck  bars  is  kept  constant,  practically 
the  same  tensile  properties  are  shown  by  all  sizes  of  wrought-iron 
rods. 

The  effect  of  previous  straining  or  cold  working  on  the  tensile 
properties  of  wrought  iron  is  to  raise  the  elastic  limit  and  ultimate 
strength  and  to  decrease  the  elongation. 

Annealing  removes  the  effect  of  overstrain  and  also  tends  to 
lower  the  elastic  limit  and  ultimate  strength  of  the  original  bar. 


WROUGHT  IRON  203 

The  following  values  are  average  results  from  tensile  tests  on 
good  grades  of  wrought  iron: 

Elastic  limit About  25,000  Ib.  per  square  inch 

Yield  point About  30,000  Ib.  per  square  inch 

Ultimate  strength About  50,000  Ib.  per  square  inch 

Elongation  in  8  in About  20  per  cent 

Reduction  in  area About  30  per  cent 

Modulus  of  elasticity About  27,000,000  Ib.  per  square  inch 

270.  Compressive  Strength  of  Wrought  Iron. — The  compres- 
sive  strength  of  wrought  iron  depends  upon  the  same  factors  as 
the  tensile  strength.     The  values  obtained  in  compression  tests 
are  about  the  same  as  those  obtained  in  tension  tests.     The 
ultimate   strength  may  be   taken   as  varying  from  45,000  to 
60,000  Ib.  per  square  inch,  and  the  yield  point  from  25,000  to 
35,000  Ib.  per  square  inch.     Overstraining  a  wrought-iron  bar 
in  tension  will  impair  its  properties  in  compression,  and  vice  versa. 

271.  Shearing    Strength    of    Wrought   Iron. — Wrought   iron 
offers  a  greater  resistance  to  shearing  forces  perpendicular  to  the 
fibers  than  it  does  to  shearing  forces  parallel  to  the  fibers.     The 
following  are  general  ranges  of  values  for  wrought  iron  in  shear 
and  torsion: 

POUNDS  PER  SQUARE  INCH 

Ultimate  shearing  strength  parallel  to  the 

fibers 20,000  to  35,000 

Ultimate  shearing  strength  across  the  fibers . .  30 , 000  to  45 , 000 

Elastic  limit  in  torsion 17,000  to  25,000 

Ultimate  strength  in  torsion 45,000  to  60,  000 

Modulus  of  elasticity  in  torsion about  12,500,000 

272.  Transverse  Strength  of  Wrought  Iron. — The  transverse 
strength  of  wrought  iron  depends  upon  the  same  factors  as  do  the 
tensile   and    compressive   strengths.     The   results   obtained   in 
cross-bending  tests  are  about  the  same  as  those  obtained  in  ten- 
sion tests.     The  yield  point  may  be  taken  as  varying  from  25,000 
to  35,000  Ib.  per  square  inch,  and  the  ultimate  strength  from 
40,000  to  60,000  Ib.  per  square  inch. 

273.  Fracture  of  Wrought  Iron. — When  good  wrought  iron 
is  broken  in  tension  or  bending,  the  fracture  is  fibrous,  and  darker 
in  color,  more  rough,  and  more  jagged  than  that  of  mild  steel. 
This  is  largely  due  to  the  presence  of  the  slag  in  the  iron.     If 
the  wrought  iron  is  broken  very  suddenly,  as  by  shocks,  sudden 
blows,  or  impact,  the  fracture  is  more  crystalline  and  granular 
in  appearance. 


204 


MATERIALS  OF  CONSTRUCTION 


274.  Welding  of  Wrought  Iron. — Welding  is  one  of  the  most 
important  properties  that  wrought  iron  possesses.  It  is  the 
joining  together  of  two  pieces  of  the  iron  by  pressing  or  hammer- 
ing them  while  at  a  very  high  temperature,  but  which  is  not  high 
enough  to  melt  the  iron.  The  ease  with  which  wrought  iron  is 


45,000 


4O,OOO 


c  35,000 


t_  30,000 


3 


25,000 
20,000 
I5,OOO 
10,000 


.OCCK  ,0004.00)6  .00  »  .(X  10 


lost 


if  Id 


Paint 


Typical  Stress-strain  Curve 

for 

Wrought  Iron 
(Curve  11  is  Portion  A-  5  of  I  Enlarged) 


.Oolg   .0014  LOOK  [OOB  LOoto  Loot  Oofa 


.02      .04     .06      .06      .10       .12       .14      .16       .\Q     .20     .22      .24     26 
Strain  Inches  per  Inch 

FIG.  91. — Typical  stress-strain  curve  for  high  grade  wrought  iron  in  tension. 


welded  is  due  to  two  things — the  absence  of  a  large  percentage 
of  impurities  such  as  carbon,  silicon,  and  sulphur,  and  the  ability 
of  the  wrought  iron  to  remain  in  a  plastic  state  (a  white  heat) 
through  a  considerable  range  of  temperature. 

It  is  very  difficult  to  make  a  good  welded  joint  because  of  the 
formation  of  iron  oxide  (melted  slag)  at  the  joint.  In  order  to 
remove  as  much  as  possible  of  this  melted  slag  in  the  welding, 
the  surfaces  of  the  two  pieces  of  iron  that  are  to  be  brought 
together  should  be  convex.  The  use  of  a  flux,  such  as  borax, 
in  welding  aids  the  work  by  making  the  slag  more  soluble  and, 
therefore,  easier  to  remove  from  the  joint. 

Care  should  be  taken  not  to  leave  the  iron  next  to  the  joint 
in  a  brittle  condition.  This  brittleness,  which  is  caused  by 
coarse  crystals,  may  be  remedied  by  working  the  wrought 
iron  under  a  hammer  or  press  until  the  critical  range  of  tem- 
perature has  been  passed. 

The  welding  temperature  in  practice  is  about  2,400  degrees 
Fahrenheit,  while  the  critical  temperature  is  about  1,275  degrees 
Fahrenheit. 


WROUGHT  IRON 


205 


The  strength  of  welded  joints  varies  from  30  to  90  per  cent  of 
the  parts  that  have  been  joined. 

275.  Miscellaneous  Properties  of  Wrought  Iron. — Wrought 
iron  has  the  important  properties  of  toughness,  ductility,  malle- 
ability, and  weldability,  but  it  cannot  be  tempered. 

The  coefficient  of  expansion  is  about  0.0000065  per  degree 
Fahrenheit. 

The  melting  temperature  is  about  2,800  degrees  Fahrenheit. 

The  specific  heat  is  0.0114. 

The  average  specific  gravity  is  7.7. 

Wrought  iron  containing  much  sulphur  is  "hot  short"  or 
"red  short,"  that  is,  the  iron  is  brittle  and  liable  to  break  when 
worked  at  a  red  heat. 

Wrought  iron  containing  much  phosphorus  is  "cold  short." 
It  has  low  ductility  when  cold,  breaks  with  a  crystalline  fracture, 
and  is  unable  to  resist  impact  stresses. 

276.  Tensile  Strength  and  Ductility  Requirements  for  Wrought 
Iron. — The  following  requirements  for  tensile  strength,  elonga- 
tion, and  reduction  in  area  for  the  different  grades  of  wrought 
iron  were  taken  from  the  American  Society  for  Testing  Materials 
Specifications  for  Wrought  Iron. 

WROUGHT  IRON  SPECIFICATION  REQUIREMENTS 


Yield 

Ultimate 

Elonga-     Reduc- 

Kind of  iron 

point, 
pounds  per 

strength, 
pounds  per 

tion  in 
8  in., 

tion  of 
area, 

square  inch 

square  inch 

per  cent 

per  cent 

Staybolt  iron           

29  ,  400  to 

49  ,  000  to 

30 

48 

31,800 

53,000 

Engine-bolt  iron 

30  000  to 

50  ,  000  to 

25 

40 

32,400 

54,000 

Refined  bar  iron  

25,000 

48,000 

22 

Wrought-iron  plate: 

6  to  24  in.  wide,  Grade  A.  .  . 

26,000 

49,000 

16 

6  to  24  in.  wide,  Grade  B  .  .  . 

26,000 

48,000 

14 

24  to  90  in.  wide,  Grade  A.  .  . 

26,000 

48,000 

12 

24  to  90  in.  wide,  Grade  B.  .  . 

26,000 

47,000 

10 

277.  Working  Stresses  for  Wrought  Iron. — It  has  'been  found 
that  a  stress  in  wrought  iron  in  excess  of  the  elastic  limit  causes  a 
permanent  set  and  raises  the  elastic  limit.  Repeated  stresses 


206 


MATERIALS  OF  CONSTRUCTION 


above  the  elastic  limit  will  cause  a  loss  of  strength  and  even 
failure  if  repeated  a  large  number  of  times.  Consequently,  the 
working  stresses  for  wrought  iron  should  never  exceed  the  elastic 
limit. 

The  following  values  of  the  allowable  unit  working  stresses  are 
for  an  average  grade  of  wrought  iron  and  should  be  increased 
about  30  per  cent  for  the  very  best  grades.  This  table  was  taken 
from  the  "American  Civil  Engineer's  Pocket  Book."  All 
values  are  given  in  pounds  per  square  inch. 

UNIT  WORKING  STRESSES  FOR  AVERAGE  WROUGHT  IRON 


Kind  of  load 

Steady 
stress 

Variable 
stress 

Shocks  and 
impact 

Tension                          .        ... 

14  ,  000 

10,000 

4,000 

Com  pression 

13  000 

9,000 

3,000 

Shear                   

10,000 

7,000 

3,500 

Torsion 

5,000 

3,500 

1,500 

Cross  bending  

12,500 

8,500 

3,500 

278.  Uses  of  Wrought  Iron. — Wrought  iron  is  used  for  spikes, 
nails,  bolts,  nuts,  wire,  chains,  chain  rods,  horseshoe  bars,  sheets, 
plates,  staybolts,  engine-bolts,  pipes,  tubing,  third  rails,  arma- 
tures, electromagnets,  and  in  the  manufacture  of  crucible  steel. 

Before  1890,  wrought  iron  was  used  very  much  in  bridge  and 
structural-building  work,  but  since  that  date  structural  steel  has 
replaced  it.  Structural  steel  costs  less  than  wrought  iron  and  is 
about  20  per  cent  stronger. 


CHAPTER  XIII 

STEEL 

A.  DEFINITIONS  AND  CLASSIFICATIONS 

279.  Definitions  of  Steel. — The  Committee  of  the  International 
Association  for  Testing  Materials  has  proposed  the  following 
definition :     Steel  is  iron  which  is  aggregated  from  pasty  particles 
without  subsequent  fusing;  is  malleable  at  least  on  some  one 
range  of  temperature;  and  contains  enough  carbon  (more  than 
0.30  per  cent)  to  harden  usefully  on  rapid  cooling  from  above 
its  critical  temperature. 

The  following  definition  proposed  by  Prof.  H.  M.  Howe  is, 
perhaps,  better  than  the  one  given  above.  Steel  is  iron  which 
is  usefully  malleable  at  least  in  some  one  range  of  temperature; 
and,  in  addition,  either  (a)  is  cast  into  an  initially  malleable  mass; 
or  (6)  is  capable  of  hardening  greatly  on  sudden  cooling;  or 
(c)  is  both  so  cast  and  so  capable  of  hardening. 

280.  Classifications  of  Steel. — Steel  may  be  classified  according 
to  method  of  manufacture,  use,  or  carbon  content. 

According  to  the  method  of  manufacture,  steel  may  be  divided 
into  cementation  steel,  crucible  steel,  acid  Bessemer  steel,  basic 
Bessemer  steel,  acid  open-hearth  steel,  basic  open-hearth  steel, 
duplex  steel,  electric  steel,  etc. 

According  to  its  use,  steel  may  be  divided  into  the  following 
classes;  structural-rivet  steel,  structural  steel,  boiler-rivet  steel, 
boiler-plate  steel,  machinery  steel,  rail  steel,  gun  steel,  axle  steel, 
spring  steel,  tool  steel,  cable-wire  steel,  etc. 

Steel  may  also  be  classified  into  carbon  or  alloy  (special)  steels, 
depending  on  the  chemical  element  which  tends  to  control  its 
strength.  Carbon  steels  may  be  divided  into  soft,  medium, 
hard,  and  very  hard  steel,  according  to  the  percentage  of  carbon 
present.  Alloy  or  special  steels  include  all  other  steels,  except 
the  carbon  steels,  and  may  be  divided  into  many  classes.  The 
name  of  each  class  depends  upon  the  name  or  names  of  the 
element  or  elements  (other  than  iron  or  carbon)  governing  its 
distinctive  properties.  Some  examples  of  alloy  steels  are:  nickel 

207 


208  MATERIALS  OF  CONSTRUCTION 

steel,  manganese  steel,  nickel-vanadium  steel,  vanadium  steel, 
chrome  steel,  etc. 

For  general  classifications  of  iron  and  steel  see  Art.  233  and 
Art.  234. 

B.  METHODS  OF  MANUFACTURE  OF  STEEL 

281.  The  Cementation  Process. — The  principle  of  this  process 
is  the  absorption  of  the  carbon  by  wrought  iron  at  a  high  red  heat 
and  thus  converting  the  wrought  iron  into  steel. 

Alternate  layers  of  charcoal  and  wrought-iron  bars  are  packed 
in  a  "  con  verting  pot"  (made  of  a  refractory  stone  or  brick)  so 
that  the  charcoal  completely  surrounds  each  bar.  Several  of 
these  pots  are  placed  in  a  furnace  and  the  temperature  gradually 
raised  to  about  1,250  degrees  Fahrenheit  at  the  end  of  3  days' 
time.  The  furnace  is  kept  at  this  temperature  from  7  to  12 
days,  depending  on  the  carbon  content  desired  in  the  steel.  When 
the  proper  amount  of  carbon  has  been  absorbed,  the  fires  are 
drawn  and  the  furnace  allowed  to  cool  slowly  for  about  a  week 
before  the  bars  are  removed. 

The  presence  of  a  little  slag  in  the  wrought-iron  bars  causes  the 
formation  of  carbon  monoxide  gas  which  makes  "  blisters"  on  the 
surface  of  the  bars,  hence  the  name  "  blister  steel"  has  been  given 
to  this  product. 

On  account  of  the  cost  and  the  length  of  time  required,  very 
little  of  this  kind  of  steel  is  made  at  the  present  time. 

282.  The  Crucible  Process. — The  principle  of  this  process  is 
the  absorption,  by  molten  wrought  iron,  of  the  carbon  in  such 
quantities  as  to  change  the  wrought  iron  into  steel. 

About  80  Ib.  of  wrought  iron  with  a  little  charcoal  and  manganese 
is  placed  in  a  closed  crucible  made  of  some  refractory  material. 
Several  of  these  crucibles  are  placed  in  a  furnace  and  subjected 
to  an  intense  heat  which  melts  the  metal  in  2  or  3  hours.  The 
crucibles  are  then  kept  in  the  furnace  for  about  half  an  hour  longer 
until  the  metal  is  " killed"  (has  ceased  to  boil  and  evolve  gases). 
After  the  "killing,"  the  crucibles  are  removed  from  the  furnace 
and  the  molten  metal  poured  into  ingot  molds.  The  time 
required  for  a  heat  varies  from  3  to  5  hours. 

As  the  cost  of  this  kind  of  steel  is  quite  high,  it  is  used  only  in 
the  manufacture  of  tools,  cutlery,  springs,  projectiles,  etc.,  where 
a  steel  of  a  high  grade  is  required. 


STEEL 


209 


283.  The  Principle  of  the  Bessemer  Process  and  the  Plant 
Equipment. — The  principle  of  the  Bessemer  process  is  the  oxida- 
tion of  the  carbon  and  some  of  the  other  impurities  by  blowing  a 
blast  of  cold  air  through  a  bath  of  molten  pig  iron  in  a  converter. 

The  essential  parts  of  the  plant  are  the  blast  furnaces  or 
cupolas,  mixers,  converters,  blowers  and  blowing  engines, 
together  with  the  necessary  ladles,  ingot  molds,  etc. 

The  molten  pig  iron  is  brought  from  the  blast  furnaces  or 
cupolas  and  stored  in  a  mixer  until  it  is  time  to  charge  the 


FIG.  92. — Diagram  of  a  Bessemer  steel  plant. 


converter.  This  mixer  is  a  large  steel  reservoir  lined  with 
firebrick.  It  has  a  capacity  of  from  100  to  600  tons  of  molten 
pig  iron  and  is  used  to  keep  the  molten  metal  hot  and  also  to  allow 
the  mixing  of  the  iron  from  several  blast  furnaces  so  as  to  secure 
the  desired  grade  of  iron. 

The  converter  is  a  bucket-shaped  vessel  of  steel  with  an  eccentric 
conical  snout.  Its  capacity  varies  from  15  to  30  tons  of  metal. 
The  converter  is  lined  with  a  refractory  material  and  is  supported 
on  trunnions  so  that  it  can  be  tipped.  The  bottom  is  pierced 
with  a  large  number  of  holes  through  which  the  air  blast  enters. 
On  account  of  the  fact  that  the  lining  in  the  bottom  burns  out 
faster  than  that  of  the  sides,  the  bottom  is  made  so  that  it  is 
detachable  and  can  be  removed  and  have  its  lining  renewed 

14 


210 


MATERIALS  OF  CONSTRUCTION 


FIG.  93. — Cross  section  of  a  mixer. 


FIG.  94. — Section    through    Bessemer    converter    while    blowing.     (Stoughtori), 


STEEL 


211 


whenever  necessary.  The  average  life  of  the  bottom  is  only 
about  25  heats.  The  lining  of  the  converter  is  of  a  siliceous 
brick  for  the  acid  process,  and  of  a  basic  material  such  as  dolomite 
or  limestone  for  the  basic  process. 

284.  The  Acid  Bessemer  Process. — About  15  or  20  tons  of 
molten  pig  iron  are  brought  in  a  ladle  from  the  mixer  and  poured 
into  the  converter  which  is  tilted  to  a  horizontal  position  to 
receive  the  charge.  Then  the  converter  is  rotated  to  a  vertical 
position  and  the  air  blast  turned  on.  This  air  blast,  under  a 


4.00% 
J.00% 
£00% 
1.00% 
0% 

. 

C.( 

tr\ 

or 

T 

*••• 

^ 

*x, 

N, 

\ 

\ 

\ 

\ 

V 

\ 

\ 

>^ 

. 

s 

^ 

-  «- 

"'/f 

\ 

s 

f^ 

^1 

"^ 

^ 

V 

^ 

s* 

9 

ii 

e<s 

e" 

- 

.^" 

••  * 

«•  . 

\ 

^ 

^ 

— 

—  "" 

£345676?       10 

Minutes  of  DJowing  End  of  Blow 

FIG.  95. — Removal  of  impurities  in  acid  Bessemer  process.     (Bradley  Stoughton.) 

pressure  of  about  25  Ib.  per  square  inch,  is  forced  through  the 
molten  iron  for  a  period  of  about  10  minutes,  after  which  time 
the  impurities  will  have  been  nearly  all  removed  by  oxidation. 

The  silicon  is  oxidized  first  with  the  evolution  of  much  heat, 
and  is  followed  by  the  oxidation  of  the  manganese.  These 
reactions  produce  an  acid  slag  which  floats  on  the  top  of  the 
metal.  The  temperature  of  the  molten  iron  now  becomes  so 
high  that  the  carbon  is  oxidized,  producing  a  brilliant  flame  that 
extends  20  or  30  ft.  above  the  mouth  of  the  converter. 

When  the  carbon  is  all  oxidized,  the  flame  drops,  the  blast  is 
turned  off,  and  the  converter  is  rotated  to  a  horizontal  position 
to  receive  a  predetermined  amount  of  speigeleisen  or  ferro- 
manganese  which  causes  the  metal  to  boil.  At  this  time  the 
carbon  passes  into  the  metal  while  the  manganese  takes  the 
oxygen  from  the  metal  and  passes  into  the  slag.  The  molten  steel 
is  then  poured  into  a  ladle  from  which  the  ingot  molds  are  filled. 


212 


MATERIALS  OF  CONSTRUCTION 


The  length  of  time  required  for  one  heat  is  about  15 
minutes. 

In  the  acid  Bessemer  process  the  pig  iron  used  must  be  low  in 
phosphorus  and  sulphur  because  neither  is  eliminated,  while  the 
silicon  content  should  be  high  in  order  to  produce  the  necessary 
heat.  The  usual  limits  of  the  composition  of  the  pig  iron  are: 
1.0  to  2.0  per  cent  of  silicon,  0.4  to  0.8  per  cent  of  manganese, 
3.5  to  4.0  per  cent  of  carbon,  0.07  to  0.10  per  cent  of  phosphorus, 
and  0.02  to  0.07  per  cent  of  sulphur. 

285.  The  Basic  Bessemer  Process. — In  this  process  a  little 
limestone  flux  is  added  to  the  charge  to  produce  a  basic  slag  that 
will  dissolve  the  silica  and  thus  prevent  it  from  attacking  the 

*  0       1       2       34        5       6       7       8       9      10      11      12      13      14min. 
3.50 


3.25 
3.00 

2.50 
2.35 
2.00 
1.75 
1.50 

LOO 


.75 
Si 

Mrr.-.-50 

S--.-25 


\ 


\ 


\ 


Mn. 

C 

S 


Ph. 


2     a 


4       fi       6       7       8       9      10     11      12      18     14  mi 

(Minutes  of  blowing.) 
FIG.  96. — Removal  of  impurities  in  basic  Bessemer  process.      (Bradley  Stoughton.') 

converter  lining.  The  impurities  are  oxidized  in  the  same  order 
as  in  the  acid  Bessemer  process  until  the  carbon  flame  drops, 
after  which  the  phosphorus  oxidizes  and  dissolves  in  the  slag 
with  the  evolution  of  a  large  amount  of  heat.  To  accomplish 
this,  the  blast  must  be  turned  on  for  about  6  minutes  longer  than 
in  the  acid  process.  If  some  manganese  is  present,  the  sulphur 
will  also  be  eliminated  from  the  iron.  In  order  to  keep  the 


STEEL 


213 


phosphorus  from  returning  into  the  metal,  the  recarburizer 
(speigeleisen  or  ferromanganese)  should  not  be  added  until  the 
metal  has  been  poured  in  a  ladle  and  the  slag  skimmed  off. 
The  total  length  of  time  required  for  a  heat  is  about  25  or  30 
minutes. 

In  the  basic  process  the  sulphur  and  phosphorus  can  be  elimi- 
nated and,  consequently,  a  pig  iron  high  in  sulphur  and 
phosphorus  can  be  used.  In  fact,  a  high-phosphorus  content  is 


FIG.  97. — Diagram  of  an  open- hearth  steel  plant. 


desirable  in  order  to  produce  the  necessary  heat.  The  limits  of 
the  composition  of  the  average  pig  iron  used  are:  1.0  to  3.0  per 
cent  of  phosphorus,  0.2  to  1.0  per  cent  of  silicon,  0.02  to  0.30  per 
cent  of  sulphur,  0.3  to  2.0  per  cent  of  manganese,  and  2.75  to  3.5 
per  cent  of  carbon. 

286.  The  Principle  of  the  Open-hearth  Process  and  the  Plant 
Equipment. — The  principle  of  this  process  is  the  oxidizing  of  the 
impurities  in  the  metal  under  the  direct  action  of  an  oxidizing 
flame  of  gas  and  air  burned  in  a  reverberatory  regenerative 
furnace. 

The  most  essential  part  is  the  furnace.  Some  of  the  other 
essential  parts  are:  ladles,  overhead  cranes,  charging  machines, 
gas  producers,  regenerators  (usually  included  with  the  furnace), 
ingot  molds,  etc. 

The  essential  parts  of  a  reverberatory  regenerative  furnace 
are: 


214 


MATERIALS  OF  CONSTRUCTION 


1.  A  large  shallow  hearth  lined  with  a  refractory  material. 
This  material  must  be  basic  or  acid  in  character,  depending  on  the 
kind  of  slag  formed. 

2.  A  cover  over  the  hearth  so  shaped  that  the  heat  produced 
by  the  combustion  of  the  gas  and  air  will  be  deflected  upon  the 
hearth. 


FIG.  98. — Section  of  an  open-hearth  furnace    showing  principle  of  operation. 

3.  Four  or  more  systems  of  brick  checkerwork  (regenerators)  ; 
two  for  heating  the  gas  and  air  while  the  other  two  are  being 
heated  by  the  escaping  burned  gases. 

4.  A  system  of  valves  and  passageways  so  that  the  admission 
of  the  gas  and  air  may  be  controlled. 

5.  A   charging  door  for  adding  the   charge  to  the  furnace. 

6.  A  tap  hole  or  spout  for  drawing  off  the  molten  metal. 
The  furnace  is  called  "  reverberatory "  because  the  flame  is 

deflected  upon  the  hearth  by  the  cover,  and  it  is  called  "  regenera- 
tive" because  the  escaping  burned  gases  are  used  to  heat  the 
brick  checkerwork. 

Two  kinds  of  open-hearth  furnaces  are  used :  (a)  the  stationary 
type  from  which  the  molten  metal  is  drawn  from  a  tap  hole;  and 
(6)  the  rolling  furnace  which  can  be  rolled  or  tilted  so  that  the 
molten  metal  may  be  discharged  through  a  spout. 


STEEL 


215 


For  fuel,  a  producer  gas  is  used.  This  gas  consists  principally 
of  nitrogen,  carbonic  oxide,  and  hydrogen.  It  is  made  by  forcing 
air  through  a  bed  of  red  hot  bituminous  coal.  Often  a  natural 
gas  is  used  for  fuel. 

287.  The  Acid  Open-hearth  Process. — The  charge,  consisting 
of  about  one-third  pig  iron  and  two-thirds  steel  scrap,  is  placed 
on  the  hearth.  The  gas  and  air  are  turned  on  and  the  temper- 
ature gradually  raised  until  the  charge  is  melting  at  the  desired 
rate.  At  the  end  of  5  or  6  hours,  the  silicon,  manganese,  and  a 
large  part  of  the  carbon  will  have  been  oxidized  out  of  the  metal. 


+JOI.     +32    3.QZ    532  53Z 
•4.17     -4/47    5.17 


(Time  of  blowing.) 

FIG.  99. — Removal   of  -impurities  in   acid   open-hearth   process.     (Bradley 

Stoughton.) 

Then  a  small  amount  of  the  metal  is  drawn  from  the  furnace  and 
a  small  test  bar  made,  from  whose  fracture  the  carbon  content  is 
estimated.  If  the  carbon  content  is  high,  some  ore  is  added  to 
produce  oxidation;  if  the  carbon  content  is  low,  some  more  pig 
iron  is  added.  Just  before  the  metal  is  drawn  off,  a  little  ferro- 
manganese  is  added  to  remove  the  oxygen  from  the  metal  and  to 
stop  any  further  oxidation  of  the  carbon.  The  charge  is  then 
conveyed  from  the  furnace  and  poured  into  ingot  molds.  The 
time  required  for  running  a  heat  varies  from  6  to  10  hours. 

The  composition  of  the  pig  iron  used  is:  0.8  to  2.0  per  cent  of 
silicon,  0.3  to  0.5  per  cent  of  manganese,  less  than  0.05  per  cent 
of  phosphorus,  less  than  0.05  per  cent  of  sulphur,  and  from 
3.0  to  4.0  per  cent  of  carbon.  The  composition  of  the  steel 
scrap  used  is:  0.1  to  0.3  per  cent  of  silicon,  0.4  to  0.8  per  cent  of 


216 


MATERIALS  OF  CONSTRUCTION 


manganese,  less  than  0.05  per  cent  of  sulphur,  less  than  0.05  per 
cent  of  phosphorus,  and  from  0.2  to  0.3  per  cent  of  carbon. 

288.  The  Basic  Open-hearth  Process. — The  charge  in  this 
basic  process  consists  of  about  equal  parts  of  pig  iron  and  steel 
scrap,  together  with  a  little  ore  and  limestone  flux.  About  3 
or  4  hours  are  required  to  melt  the  charge  and  oxidize  most  of 
the  silicon  and  some  of  the  manganese  and  carbon.  Then 


2.0 


1.0 


0.5 


s 

\ 

^^ 

^0 

*h 

\ 

-•>, 

\ 

'-• 

•^ 

v 

'v 

s^ 

\ 

*v 

^ 

\ 

g 

5 

s> 

± 

\ 

\ 

n 

\ 

\ 



•^ 

^ 

nr 

-0 

L 

% 

^ 

^^ 

^•0 

?v5~< 

- 

A 

\ 

0 

•^ 

"•>- 

^ 

1 

V 

~—  , 

c 

t\ 

\ 

\ 

tp 

SN 

\ 

\ 

\t 

—  ,^ 

^ 

/tn 

\ 

\\ 

•  —  , 

—•  ~ 

Jy> 

\ 

^ 

\ 

\ 

J£ 

--, 

~~« 

— 

••^ 

^>s, 

cV 

-^ 
Sr- 

/ 

3       4 


567 
Hours 


FIG.   100. — Removal    of    impurities    in     basic    open-hearth    process.      (Bradley 

Stoughton.) 

the  phosphorus  is  oxidized  and  absorbed  by 'the  slag,  while  some 
of  the  manganese  combines  with  some  of  the  sulphur  and  is 
dissolved  in  the  slag.  The  charge  is  tested  from  time  to  time  by 
molding  and  fracturing  a  small  test  bar.  When  the  elements 
are  reduced  to  the  proper  percentages,  the  molten  steel  is  drawn 
off  in  a  ladle.  After  the  slag  is  skimmed  off  and  a  recarburizer 
added,  as  in  the  basic  bessemer  process,  the  molten  steel  is 
poured  into  the  ingot  molds.  The  total  time  required  to  run  a 
heat  varies  from  8  to  12  hours. 

The  steel  scrap  used  in  this  process  has  about  the  same  composi- 
tion as  the  steel  scrap  used  in  the  acid  open-hearth  process, 
except  that  the  phosphorus  and  sulphur  contents  may  be  a  little 
higher.  The  composition  of  the  pig  iron  used  is:  less  than 
1.0  per  cent  of  silicon,  more  than  1.0  per  cent  of  manganese,  from 
1.0  to  2.5  per  cent  of  phosphorus,  from  0.02  to  0.30  per  cent 
of  sulphur,  and  from  2.5  to  3.5  per  cent  of  carbon. 


STEEL 


217 


Open-hearth  steel,  like  Bessemer  steel,  is  used  mostly  for  all 
kinds  of  structural  purposes. 

289.  The  Electric  Process. — The  principle  of  this  process  is 
the  same  as  that  of  the  open-hearth  process  except  that  electricity, 
instead  of  gas  and  air,  is  used  to  produce  the  heat  necessary  for 
the  oxidation  of  the  impurities.  In  the  electric  process,  no 
oxygen  is  required  to  supply  the  heat.  This  is  an  advantage 
over  all  other  processes.  The  electric  furnace  is  very  efficient 


Hcxrfh 

Z//7//2? 


FIG.  101. — Section  of  a  Heroult  arc  type  electric  furnace. 

in  removing  the  sulphur  and  the  oxygen  from  the  steel,  but  it  is 
less  efficient  in  removing  the  phosphorus. 
There  are  three  types  of  electric  furnace: 

1.  Furnaces  using  an  open  arc  between  electrodes  above  the  bath.     The 
Stassano  furnace  is  an  example  of  this  type. 

2.  Furnaces  using  an  arc  between  the  electrodes  and  the  bath.     The 
Giroud,  Heroult,  and  Keller  furnaces  are  examples  of  this  kind. 

3.  Furnaces  of  the  induction  type  in  which  the  bath  forms  the  secondary 
coil  (or  part  of  the  coil)  of  a  transformer.     The  Rochling-Rodenhauser  and 
Kjellin  furnaces  are  examples  of  this  type. 

The  power  consumption  of  an  electric  furnace  varies  from 


218  MATERIALS  OF  CONSTRUCTION 

150  to  1,000  kilowatt-hours  per  ton  of  steel  produced  according  to 
the  type  of  furnace,  kind  of  materials  in  the  charge,  and  the  tem- 
erature  of  the  charge  at  the  start.  The  time  necessary  for  a  heat 
varies  from  2  to  5  hours,  depending  upon  conditions. 

In  the  production  of  high  quality  steel,  the  electric  furnace  is  a 
strong  competitor  of  the  crucible  process,  because  it  can  produce 
larger  quantities  at  a  heat  and  at  a  slightly  lower  cost.  The 
electric  furnace  has  an  advantage  over  all  other  furnaces  in 
making  special  alloy  steels,  because  it  does  not  need  to  be  operated 
under  oxidizing  conditions.  However,  the  electric  furnace 
cannot  compete  in  cost  with  the  bessemer  and  open-hearth 
processes  in  the  production  of  steel  of  a  medium  or  low  quality. 

290.  The  Duplex  Process. — This  process  is  usually  a  combi- 
nation of  the  acid  Bessemer  and  basic  open-hearth  processes.     The 
molten  pig  iron  is  first  placed  in  the  Bessemer  converter  until 
the  silicon,  manganese,  and  most  of  the  carbon  are  oxidized.     Then 
the  molten  metal  is  removed  from  the  converter  and  placed  in 
a    basic   open-hearth  furnace   where   the   phosphorus   and   the 
remainder  of  the  carbon  are  removed.     The  recarburizer  is  added 
to  the  steel  in  the  ladle  after  the  slag  has  been  skimmed  off,  as 
in  the  basic  open-hearth  process.     The  total  time  required  for 
a  heat  is  about  6  or  8  hours. 

The  advantages  of  the  duplex  process  are:  a  low-grade  pig 
iron  with  a  high  phosphorus  content  may  be  used;  a  steel  is  pro- 
duced that  is  better  in  quality  than  the  Bessemer  steel;  the  time 
required  for  a  heat  is  about  half  the  time  required  by  the  basic 
open-hearth  process. 

Another  kind  of  duplex  process  is  where  the  preliminary 
refining  of  the  steel  is  done  in  a  Bessemer  converter  or  an  open- 
hearth  furnace  and  the  final  refining  in  an  electric  furnace. 
This  process  gives  a  steel  of  a  high  quality  and  at  a  lower  cost 
than  when  the  electric  process  is  used  alone. 

291.  The  Triplex  Process. — In  this  process  the  molten  metal  is 
taken  from  a  mixer  and  placed  in  an  acid  Bessemer  converter 
where  the  silicon,  carbon,  and  manganese  are  nearly  all  removed. 
Then  the  molten  metal  is  transferred  to  a  basic  open-hearth 
furnace  where  the  phosphorus  is  removed  and  the  steel  recar- 
burized.     After  this,  the  molten  steel  is  placed  in  an  electric 
furnace  for  the  final  refining;  that  is,  for  the  removal  of  the  sulphur 
and  the  oxygen.     The  triplex  process  gives  a  very  high-grade 
steel  and  is  less  expensive  than  the  electric  process. 


STEEL 
292.  Comparison  of  the  Different  Processes.— 


219 


Quality 

Cost 

Length  of  time 
for  one  heat 

Total  quantity 
produced 

1.  Electric  
2  Triplex 

Crucible 
Electric 

Basic  open-hearth 
Acid  open-hearth 

Basic  open-hearth 

3  Crucible 

Triplex 

Triplex 

4.  Basic  open-hearth  
5.  Acid  open-hearth  
6.  Duplex  (usual)  
7.  Basic  Bessemer  
8  Acid  Bessemer 

Acid  open-hearth 
Basic  open-hearth 
Duplex  (usual) 
Basic  Bessemer 
Acid  Bessemer 

Duplex  (usual) 
Crucible 
Electric 
Basic  Bessemer 

Acid  open-hearth 
Crucible 
Duplex  (usual) 
Electric 
Triplex 

C.  COMPLETING  THE  MANUFACTURE  OF  THE  STEEL 

293.  Casting  the  Ingots. — Most  of  the  steel  is  cast  into  ingots, 
which  are  about  7  ft.  high,  18  in.  square  at  the  bottom,  and  about 
15  in.  square  at  the  top. 

The  ingot  molds  are  placed  on  small  flat  cars  that  run  on  a 
track.  At  the  proper  time  the  molten  steel  is  drawn  from  the 
furnace  into  a  ladle  which  is  a  bucket  shaped  vessel  of  steel  lined 
with  a  refractory  material  and  having  a  valve  at  the  bottom. 
The  cars  carrying  the  ingot  molds  are  run  under  the  ladle,  and 
each  mold  is  filled  by  means  of  the  valve.  The  cars  then  pass 
under  cranes  that  remove  the  molds  from  the  ingots.  The 
molds  are  washed  with  clay  water  to  prevent  the  steel  from 
sticking  to  them,  and  are  used  again.  The  ingots  pass  on  to  a 
"soaking  pit"  or  a  reheating  furnace.  The  average  life  of  an 
ingot  mold  is  about  100  casts. 

294.  Defects  in  Ingots. — When  the  ingots  cool,  they  form  a 
structure  that  is  not  very  homogeneous  as  the  metal  on  the  outside 
cools  first  so  that  when  the  metal  of  the  inside  cools  and  shrinks, 
a  cavity  or  pipe  is  formed  inside  the  ingot  and  near  its  upper  end. 
Oxides  of  phosphorus,sulphides  of  iron, and  sulphides  of  manganese, 
together  with  some  carbon,  tend  to  segregate  near  the  upper  por- 
tion of  the  central  part  of  the  ingot.     The  gases  and  slag  in  the 
molten  metal  rise  to  the  top  of  the  ingot  and  form  blowholes. 
Ingotism  is  the  formation  of  large  crystals  of  steel  and  is  caused 
by  slow  cooling  or  by  casting  at  too  high  a  temperature. 

Piping  and  segregation  may  be  overcome  by  a  proper  propor- 
tioning of  the  different  elements,  while  the  only  remedy  for 
blowholes  is  to  cut  off  the  top  of  the  ingot.  Careful  rolling  and 
forging  will  remove  the  bad  effects  of  ingotism  by  reducing  the 
size  of  the  steel  crystals. 


220  MATERIALS  OF  CONSTRUCTION 

295.  Reheating  the  Ingots. — For  good  working,  it  is  necessary 
for  the  ingot  to  have  the  proper  working  temperature  throughout. 
As  the  outside  of  the  ingot  cools  more  rapidly  than  the  interior, 
it  is  necessary  to  place  the  ingot  in  a  furnace  where  the  outside 
of  the  ingot  may  be  heated  and  kept  at  the  proper  temperature 
for  working  until  the  interior  has  solidified  and  cooled  to  that 
temperature.     If  the  ingot  becomes  too  cool  during  the  working, 
it  is  necessary  to  stop  and  reheat  it  before  going  on  with  the 
working. 

The  furnaces  used  for  reheating  purposes  are  of  three  types: 
the  "  soaking  pit,"  the  regenerative  gas-fired  pit  furnace,  and  the 
billet  heating  furnace. 

The  "  soaking  pit "  is  a  pit  in  which  the  ingot  is  charged  through 
the  top  and  kept  in  a  vertical  position.  The  purpose  of  the 
soaking  pit  is  to  equalize  the  temperature  of  the  ingot.  No  fuel 
is  used,  the  interior  of  the  hot  ingots  supplying  the  heat.  The 
soaking  pit  is  used. to  equalize  the  temperature  of  the  ingot  before 
the  working  is  commenced. 

The  regenerative,  gas-fired,  pit  furnace  is  a  vertical  furnace 
using  gas  for  fuel.  The  ingot  is  charged  through  the  top,  and 
remains  in  the  furnace  until  it  is  heated  to  the  proper  work- 
ing temperature.  This  furnace  can  be  used  for  equalizing  the 
temperature  of  the  ingot  and  also  for  reheating  the  ingot  when  it 
cools  during  the  working. 

The  billet  heating  furnace  is  a  horizontal  gas-fired  furnace  in 
which  the  billets  enter  at  the  cool  end  of  the  furnace  and  are 
pushed  through  by  means  of  a  hydraulic  ram,  discharging  from 
the  hot  end.  This  furnace  is  used  for  heating  small  pieces  of  steel 
either  before  or  during  the  working. 

296.  Rolling. — The   rolling   is   done   by   rolling   mills   which 
consist  essentially  of  two  (two  high)  or  three  (three  high)  layers 
of  smooth  chilled  cast-iron  rollers  of  the  desired  form.     Some- 
times a  mill  has  a  set  of  vertical  rollers,  placed  just  outside  the 
horizontal  ones,  which  keep  the  edges  of  the  metal  smooth  but  do 
not  reduce  it.     Such  a  mill  is  called  a  universal  mill. 

The  ingot  passes  through  the  rolls  many  times  (from  2  to  20) 
before  emerging  in  the  desired  form,  each  passage  through  the 
rolls  changing  the  shape  of  the  steel  somewhat.  The  action  of 
the  rollers  compresses  the  metal  under  the  rollers  and  also  tends 
to  produce  longitudinal  tension  in  the  surface  fibers  of  the  steel. 
The  speed  of  rolling  is  quite  great,  varying  from  a  few  miles  per 


STEEL 


221 


hour  for  special  shapes,  to  about  10  miles  per  hour  for  rails,  and  to 
as  high  as  30  miles  per  hour  for  rods.  Too  great  a  speed  in  rolling 
causes  a  heating  of  the  steel,  due  to  the  rapid  distortion.  Rolling 


HM*i«ll 


FIG.  102. — "Three  High"  I-beam  roughing  rolls. 


FIG.   103.— "Three  High"  I-beam  finishing  rolls. 

mills  produce  plates,  bars,  structural  steel  shapes,  rails,  and  rods. 

297.  Forging  and  Pressing. — Forging  steel  is  working  it  under 
a  hammer  until  it  is  of  the  desired  size  and  shape.  Most  of 
the  hammers  used  at  the  present  time  are  steam  hammers,  and 
they  vary  in  size  from  a  few  hundred  pounds  up  to  30  or  50  tons. 

Drop  forgings  are  forgings  made  by  using  dies  in  connection 
with  the  steam  hammer.  The  metal  usually  passes  through  a 


222 


MATERIALS  OF  CONSTRUCTION 


series  of  dies  before  becoming  of  the  proper  size,  shape,  and 
finish. 

Forging  may  also  be  done  by  using  a  hydraulic  press  instead  of 
a  steam  hammer.  With  the  hydraulic  press  the  force  is  applied 
more  slowly  and  acts  for  an  appreciable  length  of  time,  while  with 
a  hammer  the  force  is  applied  as  a  blow.  Hydraulic  presses 
vary  in  size  from  a  few  tons  pressure  up  to  1,400  tons  pressure  or 
more. 

The  mechanical  treatment  of  an  ingot,  such  as  forging,  pressing, 
drawing,  or  rolling,  greatly  improves  the  quality  of  the  steel  by 
solidifying  the  metal,  reducing  the  blowholes,  and  increasing  the 


FIG.  104.— Rolling  mills.     (Illinois  Steel  Co.) 

strength  and  specific  gravity.  For  the  best  results,  the  work 
should  be  done  when  the  ingot  has  cooled  to  a  low-red  heat. 
Forging  works  the  metal  better,  but  it  is  more  expensive  and 
less  rapid  in  operation  than  rolling.  Much  more  steel  is  made  by 
rolling  than  by  forging. 

298.  Wire  Drawing. — In  making  wire,  the  steel  is  first  rolled 
in  rods  and  then  these  rods  are  drawn  through  holes  in  a  plate. 
These  holes  vary  in  size  from  the  diameter  of  the  rod  down 
to  the  diameter  of  the  desired  wire.  Some  thick  lubricant  is 
used  to  reduce  friction  and  to  prevent  wear  of  the  holes  in 
the  draw  plate.  The  diameter  of  the  rolled  rods  is  usually  from 


STEEL  223 

H  to  M  in-  The  sectional  area  of  the  rod  is  reduced  about  20 
or  25  per  cent  for  each,  hole  that  it  is  pulled  through.  Cold 
drawing  makes  the  metal  very  hard,  and  it  must  be  annealed  to 
a  low-red  heat  after  it  has  been  drawn  from  3  to  10  times.  The 
number  of  drawings  through  the  holes  depends  upon  the  original 
diameter  of  the  rod  and  the  desired  diameter  of  the  wire,  and 
may  be  as  many  as  20  or  more. 

D.  HEAT  TREATMENT  OF  STEEL 

299.  Hardening  of  Steel. — The  heat  treatment  of  steel  by 
hardening,    tempering,    and    annealing    greatly    influences    its 
physical  properties.     Every  steel  has  a  certain  "critical"  tem- 
perature in  the  range  of  which  important  molecular  changes 
occur  in  heating  and  cooling.     In  general,  this  range  is  from  a 
low-yellow  heat  down  to  a  dull-red  heat. 

Steel  is  hardened  by  heating  it  up  to  this  critical  temperature, 
which  is  usually  between  1,250  and  1,600  degrees  Fahrenheit, 
and  then  retarding  the  molecular  changes  that  occur  in  slow 
cooling  by  suddenly  plunging  the  steel  into  molten  lead,  oil, 
water,  ice  water,  or  iced  brine,  etc.,  according  to  the  degree  of 
hardness  desired.  The  hardness  increases  with  the  rate  of  cool- 
ing, and,  in  general,  the  cooler  the  quenching  liquid,  the  harder 
the  steel.  The  degree  of  hardening,  as  well  as  the  critical  tem- 
perature, also  depends  to  some  extent  upon  the  amount  of  carbon, 
manganese,  chromium,  tungsten,  and  other  elements  present. 

300.  Tempering  of  Steel. — As  some  hardened  steels  are  too 
brittle  to  use,  they  must  be  tempered  to  reduce  the  hardness  to 
some   extent.     "Tempering"   is   accomplished   by  heating  the 
steel  up  to  a  temperature  which  is  less  than  the  critical  tempera- 
ture, and  then  quenching  it  in  some  liquid  as  oil,  water,  etc. 
For  most  steels,  the  temperature  for  tempering  varies  from  425 
to  600  degrees  Fahrenheit.     This  temperature  is  indicated  by  the 
color  of  the  film  of  oxide  that  forms  on  the  surface  of  the  steel. 
This    color    varies    from    a    pale-yellow    (about  425    degrees 
Fahrenheit)  through  straw,  brown,  purple,  and  blue  to  dark- 
blue  (about  600  degrees  Fahrenheit).     Tempering  the  steel  tends 
to  increase  its  ultimate  strength. 

301.  Annealing  of  Steel. — Annealing  consists  of  heating  the 
steel  up  to  a  light  red  heat  and  then  allowing  it  to  cool  very 
slowly  for  some  (2  or  3)  days.     The  usual  annealing  tempera- 


224  MATERIALS  OF  CONSTRUCTION 

ture's  are  between  400  and  900  degrees  Fahrenheit.  If  the  size 
of  grain  is  to  be  reduced  much,  the  temperature  must  be  raised 
slightly  above  the  lower  limit  of  the  critical  range  of  temperature. 
The  heating  must  be  done  in  such  a  way  that  the  steel  will  not 
come  in  contact  with  the  fuel  and  flames,  and  the  pieces  of  steel 
must  be  supported  so  that  they  will  not  warp.  Small  pieces  are 
often  packed  in  charcoal  in  closed  iron  boxes. 

Annealing  removes  any  overstrain  caused  by  the  cooling  or  by 
the  working  of  the  steel;  reduces  the  size  of  the  grains  of  the  steel; 
makes  the  steel  soft  and  ductile ;  and  reduces  the  elastic  limit  and 
ultimate  strength. 

302.  Case    Hardening  of  Steel. — Case  hardening  is  accom- 
plished by  heating  soft  or  medium  steel  in  contact  with  carbon 
so  that  the  carbon  will  penetrate  the  outer  skin  of  the  steel. 
The  temperature  required  is  about  1 ,650  degrees  Fahrenheit.     The 
time  varies  from  2  to  12  hours  according  to  conditions.     The 
penetration  of  the  carbon  is  usually  less  than  ^  in. 

Case  hardening  produces  a  high-carbon  steel  surface!  which  is 
hard  and  which  will  resist  wear,  abrasion,  cutting,  and  indenta- 
tion, while  the  interior  is  left  soft  and  tough  and  capable  of 
resisting  impact. 

Harveyized  armor  plate  is  made  by  case  hardening  the  side  of 
an  armor  plate  of  tough  medium  steel. 

E.  STRUCTURE  AND  CONSTITUTION  OF  STEEL 

303.  Normal    Constituents    and    Compounds. — The    normal 
constituents  of  iron  and  steel  are  ferrite  (pure  iron),  cementite 
(Fe3C),    and   graphite    (free   amorphous   carbon).     These    con- 
stituents appear  in  various  forms  and  combinations  when  the 
iron  or  steel  is  in  the  solid  and  liquid  forms,  depending  upon  the 
amount  of  carbon,  rate  of  cooling,  presence  of  other  elements, 
etc. 

Molten  steel  is  a  solution  of  liquid  carbide  of  iron  in  liquid  iron 
whose  carbon  content  is  less  than  about  2.0  per  cent  (some 
authorities  claim  1.7  per  cent  and  others  2.2  per  cent).  If  the 
carbon  content  were  over  2.0  per  cent,  the  liquid  solution  would  be 
called  molten  cast  iron.  When  the  carbon  is  less  than  2.0  per 
cent,  there  is  no  separation  of  the  constituents  when  the  solution 
cools,  i.e.,  it  forms  a  " solid"  solution.  Steels  are  solid  solutions. 

When  a  molten  mixture  cools,  one  constituent  may  solidify 


STEEL 


225 


before  another,  or  before  the  solution  freezes  as  a  whole.  If  the 
proportioning  of  the  parts  is  such  that  the  freezing  point  of  the 
solution  is  reached  before  that  of  any  of  its  parts,  it  is  called  a 
"eutectic"  solution,  in  the  case  of  the  cast  irons,  and  a  "eutec- 


CAST 


± 


IRQ"5 


H,YPER- 


LIQUID  SOLUTION 


N^ 


CEMENTITE 


£ 


D        Freezing 


EUTECTIC  ALLOY  (SATURATED  IAUSTENITE  +CEMENTITE) 
Decomposing    into    Iron  |     and     Graphite 


I  AUSTENITE 


CEME  NTrrd 


I  EUTECTIC 


AUSTENITE 
CEMENTITE 


EUTECTIC 


(AUSTENITE 

I  CEMENTITE 


l  I       I 

1  I  FtRRITt  +  CEMENTITE  |(WMITECAST  IRON3J 

I  n  FCRRITE  + GRAPHITE   I       KRARE)    | 

;RRITE  +PtARLITE    +  GRAPHITE  (6RAY  CAST 


PEARLITE  •  PEARLITE   ' 

!       I       ! 


fe)|WiTh  Hypo    Eutectokj   matrix. 
I       (b^WiTh  Hyper  EuTecToid    JmaTrix. 


CEMENTITE 
I          I 


PEARLITE 


2.0  JO  40   433          3.0  6,0  8.67  *C 

30  49  60  73  90  lOO%fe,C 

PERCENTAGE    COMPOSITION 


FIG.   105. — Roberts- Austen    iron-carbon    diagram.     (Slightly    modified.) 


toid"  solution  in  the  case  of  the  steels.  The  substance  formed 
by  the  freezing  of  the  eutectic  solution  is  called  the  "eutectic," 
while  that  formed  by  the  freezing  of  the  eutectoid  solution  is 
called  the  "  eutectoid."  If  there  is  an  excess  of  iron  carbide 
(Fe3C)  present,  the  steel  solution  is  called  "  hyper-eutectoid " 

15 


226  MATERIALS  OF  CONSTRUCTION 

and  the  cast-iron  solution  "hyper-eutectic."  But  if  there  is  an 
excess  of  free  iron  present,  the  steel  or  solid  solution  is  called 
"hypo-eutectoid "  and  the  cast-iron  solution  "hypo-eutectic." 

304.  Critical  Temperatures. — It  has  been  found  that  when  a 
bar  of  soft  steel  containing  about  0.20  per  cent  of  carbon  is 
gradually  heated,  the  temperature  of  the  bar  increases  regularly 
with  the  time  up  to  a  certain  point,  Aci,  at  which  the  increase 
in  temperature  is  retarded  for  a  short  time.  After  this  the 
temperature  will  again  increase  regularly  until  a  second  point, 
Ac2,  is  reached,  where  a  similar  retardation  will  occur.  If  the 
heating  is  continued,  a  third  such  point,  Ac3,  will  be  found  before 
the  steel  melts. 

In  cooling,  the  same  thing  will  happen  but  in  the  reverse 
order,  the  " critical"  points  found  being  called  Ar3,  Ar»,  and  Ar\. 
These  latter  points  are  each  about  55  degrees  Fahrenheit 
lower  than  the  corresponding  points  obtained  when  the  bar  is 
heated. 

If  the  carbon  content  is  increased,  the  point  Ars  tends  to 
approach  point  Ar2  and  will  finally  coincide  with  it.  A  further 
increase  in  the  carbon  content  will  tend  to  make  the  point  Ar2-z 
approach  the  point  Ari,  and,  if  the  carbon  is  increased  sufficiently, 
all  three  of  these  points  will  coincide.  This  is  also  true  in  regard 
to  the  points  Ac3,  Acz,  and  Aci. 

When  a  high-carbon  steel  is  gradually  cooled,  the  temperature 
will  decrease  regularly  until  the  point  Ari_2-3  is  reached,  and 
then  there  will  be  a  sudden  momentary  increase  in  temperature, 
after  which  the  regular  rate  of  cooling  will  be  resumed.  This 
phenomenon  is  called  "recalescence,"  and  the  point  the 
"recalescence  point." 

An  explanation  of  this  phenomenon  is  that  there  is  a  change  in 
the  molecular  structure  of  the  steel  at  each  of  these  critical 
points.  The  iron  above  the  Ar3  point  is  called  gamma  iron;  the 
iron  between  the  Ar%  and  the  Ar2  points,  beta  iron;  and  the  iron 
between  the  Ar2  and  the  Ar\  points,  alpha  iron. 

The  Ari  point  is  at  about  1,275  degrees  Fahrenheit,  while  the 
Ar2  point  varies  between  1,400  to  1,275  degrees  Fahrenheit,  and 
the  Ar3  point  from  1,650  to  1,400  degrees  Fahrenheit  (after 
which  it  coincides  with  Arz)  according  to  the  carbon  content. 
Increasing  the  carbon  content  lowers  Ar3  until  it  coincides  with 
Ar2,  and  increasing  the  carbon  content  still  further  causes  Ar2-« 
to  be  lowered  until  it  coincides  with 


STEEL  227 

Alpha  iron  is  soft,  ductile,  and  magnetic,  while  -beta  iron  is 
hard,  glassy,  brittle,  and^  non-magnetic. 

305.  Slow  Cooling  of  Molten  Steel. — When  steel  cools  slowly, 
it  passes  from  a  liquid  solution  of  iron  carbide  in  gamma 
iron  through  austenite,  martensite,  troostite,  and  sorbite 
to  pearlite.  It  will  be  all  pearlite  if  the  solution  is  a  eutectoid 
solution. 

If  there  is  an  excess  of  gamma  iron  present  (hypo-eutectoid), 
this  excess  will  gradually  separate  out  in  the  form  of  ferrite 
before  the  pearlite  is  formed.  This  ferrite  passes  from  gamma 
iron  to  beta  iron  and  then  into  alpha  iron.  At  the  Ar\  point, 
pearlite  is  formed,  and  the  excess  iron  will  be  in  the  form  of 
ferrite  (probably  a  mixture  of  alpha  and  beta  irons).  Thus  the 
resulting  steel  will  be  a  mixture  of  ferrite  and  pearlite. 

If  there  is  an  excess  of  iron  carbide  in  the  solution,  this  excess 
will  separate  out  as  cementite  until  the  solution  is  eutectoid  in 
character  and  until  the  point  Ar\  is  reached,  when  the  remainder 
of  the  solution  will  freeze  as  pearlite,  the  resulting  steel  being  a 
mixture  of  pearlite  and  cementite. 

Austenite  is  a  solid  solution  of  iron  carbide  (cementite)  and 
gamma  iron.  It  is  stable  above  the  Ar\  point,  may  contain 
carbon  up  to  about  2.0  per  cent,  and  is  unmagnetic,  ductile,  and 
very  hard. 

Martensite  is  the  first  stage  in  the  transformation  of  austenite. 
The  structure  of  martensite  is  needlelike,  and  is  much  harder 
than  austenite.  Martensite  is  not  very  stable.  The  iron  is  a 
mixture  of  the  alpha  and  beta  forms. 

Troostite  is  the  next  stage  following  martensite.  Troostite  is 
not  stable.  It  is  not  quite  so  hard  as  martensite,  probably 
because  the  proportion  of  alpha  iron  has  been  increased. 

Sorbite  is  the  last  stage  before  pearlite.  Sorbite  is  softer  than 
troostite  and  harder  and  much  stronger  than  pearlite. 

Pearlite  is  the  last  stage  in  the  transformation  of  austenite. 
Pearlite  is  a  mixture  of  6  parts  of  ferrite  and  1  part  of  cementite, 
and  it  is  less  hard,  less  strong,  and  more  ductile  than  the  other 
forms  of  austenite.  Pearlite' is  quite  stable  below  An,  except  that 
the  cementite  tends  to  form  ferrite  and  graphite. 

306.  Rapid  Cooling  of  Molten  Steel. — In  the  rapid  cooling  of 
molten  steel  the  molecules  do  not  have  time  to  go  through  all  of 
the  successive  transformations  that  they  do  in  the  case  of  slow 
cooling.  Hence,  various  arrangements  of  the  constituents  will 


228  MATERIALS  OF  CONSTRUCTION 

be  found  in  the  final  structure  of  the  steel  due  to  the  rate  of  cool- 
ing, initial  temperature,  amount  of  carbon,  and  amounts  of  other 
elements  present.  Hypo-eutectoid  steel  will  always  have  free 
ferrite  present  with  the  other  constituents,  while  free  cementite 
will  be  found  in  the  case  of  hyper-eutectoid  steel. 

Rapid  cooling  or  quenching  (as  in  water)  of  a  solution  of  molten 
steel  will  give  a  steel  whose  constitution  will  be  austenite  with 
some  martensite.  Very  rapid  cooling,  as  by  quenching  in  ice 
water,  from  the  temperature  Tl,  at  which  austenite  begins  to 
form,  will  give  the  same  results. 

A  little  slower  rate  of  cooling  from  a  molten  steel  solution,  or  a 
rapid  cooling  from  the  temperature  T2  (of  the  formation  of 
martensite)  gives  a  steel  consisting  mostly  of  martensite  with 
some  austenite  or  troostite  or  both. 

A  slower  rate  of  cooling  (as  quenching  in  air)  from  a  molten 
steel  solution,  or  a  rapid  cooling  from  the  temperature  T3,  of 
the  formation  of  troostite,  will  give  a  steel  consisting  essentially 
of  troostite  with  some  martensite  but  with  no  sorbite. 

A  very  slow  cooling  of  a  molten  steel  solution,  or  a  rapid  cooling 
from  the  temperature  T4,  of  the  formation  of  sorbite,  gives 
sorbite  steel  which  may  contain  some  pearlite. 

If  slow  cooling  is  carried  to  the  temperature  T5  (of  the  forma- 
tion of  pearlite),  the  constitution  of  the  resulting  steel  will  be 
mainly  pearlite,  except  that  some  sorbite  will  be  present  if  the 
steel  is  suddenly  cooled  from  a  temperature  very  close  to  Ar\. 

Temperatures  Tl,  T2,  773,  and  T4  are  all  above,  while  the 
temperature  T5  is  slightly  below,  the  point  Ar\. 

307.  An  Explanation  of  the  Hardening  of  Steel. — It  is  thought 
that  the  hardness  of  steel  and  iron  depends  upon  the  amount  of 
beta  iron  present,  and  that  any  treatment  which  will  increase 
the  amount  of  beta  iron  present  will  also  increase  the  hardness. 
An  increase  in  the  carbon  content  increases  the  hardness  prob- 
ably because  the  carbon  tends  to  hold  the  iron  in  the  beta  form 
and  prevent  its  transformation  into  the  softer  alpha  iron.     Sud- 
den  cooling,  from  the  temperature  of  the  formation  of  beta 
iron,   does  not  give  the  beta  iron  time  for  all  of  it  to  change 
into  the  alpha  form;  and  the  quicker  the  cooling,  the  less  the 
change. 

308.  An  Explanation  of  the  Tempering  of  Steel. — In  ordinary 
commercial  tempering,   the   steel  is   heated   to   a   temperature 
varying  from  425  to  600  degrees  Fahrenheit,  and  then  quenched. 


STEEL  229 

The  quenching  is  done  to  prevent  the  temperature  from  increas- 
ing above  the  desired  degree. 

The  transformation  of  one  constituent  to  another  depends 
upon  the  temperature  reached,  the  rate  of  increase  in  temperature, 
and  the  length  of  time  that  the  steel  is  held  at  that  temperature. 
In  heating  cold  steel,  the  austenite  will  be  all  changed  to  marten- 
site  when  400  degrees  Fahrenheit  is  reached,  and  the  martensite 
will  be  changed  to  troostite  before  750  degrees  Fahrenheit  is 
reached.  Further  heating  changes  the  troostite  to  sorbite, 
sorbite  alone  existing  above  1,100  degrees  Fahrenheit.  Conse- 
quently, in  commercial  tempering,  the  resultant  steel  will  be 
troostite,  with  some  ferrite  or  cementite,  depending  on  the  carbon 
content.  Only  austenite,  martensite,  austen-troostite,  and 
marten-troostite  steels  can  be  tempered,  the  commercial  process 
having  no  effect  on  troostite  or  trooso-sorbite  steels. 

309.  An  Explanation  of  the  Annealing  of  Steel. — In  annealing, 
the  steel  is  heated  to  higher  temperatures  than  in  tempering  and 
is  allowed  to  cool  very  slowly.  This  gives  a  steel  which  may 
be  essentially  sorbite  or  pearlite  (though  some  troostite  may  be 
present  if  the  annealing  temperature  is  low)  which  is  softer  and 
more  ductile,  though  less  strong,  than  the  martensite,  austenite, 
or  troostite.  Ordinary  annealing  temperatures  vary  from  400  to 
900  degrees  Fahrenheit'. 

To  reduce  the  coarse  crystallization  in  the  steel,  the  annealing 
temperature  must  be  above  the  critical  point,  say  from  1,700  to 
1,450  degrees  Fahrenheit,  depending  upon  the  carbon  content. 
Some  think  that  in  annealing,  most  all  of  the  beta  iron  present 
is  changed  over  into  the  alpha  form. 


F.  PHYSICAL    AND    MECHANICAL    PROPERTIES    AND    USES    OF 

STEEL 


310.  General. — The  physical  and  mechanical  properties  of  steel 
depend  upon  the  methods  of  manufacture,  mechanical  working, 
heat  treatment,  and  chemical  composition. 

The  principal  chemical  elements  affecting  the  properties  of 
steel  are  carbon,  silicon,  sulphur,  phosphorus,  and  manganese. 
Other  chemical  elements  are  present,  but  usually  in  such  small 
quantities  that  they  have  practically  no  effect  on  the  properties 
of  the  steel.  Some  chemical  elements,  such  as  nickel,  chromium, 


230 


MATERIALS  OF  CONSTRUCTION 


copper,  vanadium,  etc.,  when  present  in  appreciable  quantities, 
also  have  their  effect  on  the  properties  of  steel.  The  effect  of 
these  elements  will  be  considered  in  the  paragraphs  on  special 
and  alloy  steels. 

311.  Effect  of  Carbon. — Carbon  has  a  very  great  effect  on  the 
physical  properties  of  steel,  depending  on  the  amount  present  and 


t  160,000 
150,000 
§  t  140,000 

s  ft  uo,ooo 

^120,000 
110,000 
100,000 
90,000 
,60,000 
70,000 
60,000 

^•^5  50,000 
^4i  40,000 
^^5  C50.000 
X  d  20,000 
^  10,000 


1 

\ 

ffOATION  6ETWEEN  TENSILE  STRENGTH 

^ 

tt 

ru 

0f 

) 

AND  YIELD  POINT 
AND 
PERCENTAGE  Of  CARBON  IN  5 

f? 

.  r^ 

~j 

V  t 

^9 

i 

)(/ 

^s 

^1, 

/u 

^ 

X 

^ 

r 

$ 

o 

s 

0 

Lh 

. 

x^ 

$ 

re 

^ 

/' 

^ 

-## 

-£ 

^ 

j 

4 

% 

^ct 

^/ 

.> 

W 

/* 

a^| 

^('/ 

> 

E 

~t 

Ifi 

K 

* 

^—* 

*** 

i 

I 

<?c 

In 

/  = 

0 

Z-- 

0 

o 

y 

•*•  "o 

^*" 

.10    .20    .JO  .40   .50  .60   .70  .60  .90   1.00  LIO    120 

Percentage  of  Carbon 

FIG.   106. — Effect  of  carbon  on  tensile  strength  of  steel. 


also  upon  its  chemical  composition  with  the  steel.  Carbon 
makes  the  steel  hard  and  strong,  but  decreases  the  ductility. 
Steel  may  be  classified  according  to  the  amount  of  carbon  in  it. 


CLASSIFICATION  OF  CARBON  STEELS 


Kind 

Per  cent  of 
carbon 

Characteristics 

Soft  steel 

0  10  to  0  20 

Not  temperable      Easy  to  weld. 

Medium  steel  

0  .  20  to  0  .  40 

Hard  to  temper.     Weldable. 

Hard  steel                

0  .  40  to  0  .  70 

Temperable.     Hard  to  weld. 

Very  hard  steel 

0  70  to  1  20 

Easy  to  temper      Not  weldable. 

The  following  formulas  are  some  approximate  ones  showing 
the  relation  of  the  carbon  content  to  the  tensile  strength  and 
ductility  of  steel: 


STEEL  231 

Average  steel, 

Yield  point  =  30,000  +  50,000  X  per  cent  C. 

Ultimate  tensile  strength  =  45,000  +  105,000  X  per  cent  C. 

Per    cent    elongation    in    8    in.  =  58  —  (Ultimate    tensile 

strength  -f-  2,500). 
Per  cent  elongation  in  8  in.  =  1,500,000  -f-  ultimate  tensile 

strength. 

The  last  formula  is  one  proposed  by  the  American  Society  of 
Civil  Engineers  and  has  been  used  in  many  specifications  for  steel. 
It  gives  elongations  that  are  too  great  for  hard  and  very  hard 
carbon  steels,  hut  it  is  fairly  accurate  for  medium  and  soft 
steels. 

Acid  open-hearth  steel, 

Ultimate       tensile        strength  =  45,000  +  (108,000  X  per 

cent  C). 
Basic  open-hearth  steel, 

Ultimate        tensile        strength  =  45,000  +  (90,000  X  per 

cent  C). 
If  the  percentages  of  phosphorus  and  manganese  are  known, 

then, 
Acid  open-hearth  steel, 

Ultimate  tensile  strength  =  40,000  +  (68,000  X  per  cent  C) 
+  (100,000  X  per  cent   P)  +  (80,000  X  per   cent   CM). 
Basic  open-hearth  steel, 

Ultimate  tensile  strength  =  38,800  +  (65,000  X  per  cent  C) 
+  (100,000  X  per  cent  P)  +  (9,000  X  per  cent  M)  + 
(40,000  X  per  cent  CM). 

312.  Effect  of  Silicon,  Sulphur,  Phosphorus  and  Manganese. 

Silicon. — The  amount  of  silicon  that  is  usually  present  in  steel 
is  less  than  0.25  per  cent,  and  up  to  this  amount  it  has  practically 
no  effect  on  the  steel.  A  larger  amount,  say  0.3  or  0.4  per  cent 
increases  the  hardness,  yield  point,  and  ultimate  strength  with 
practically  no  reduction  in  the  ductility.  If  the  steel  contains 
more  than  1.0  per  cent  of  silicon,  it  is  called  silicon  steel. 

Sulphur. — Within  the  limits  common  to  ordinary  steel 
(0.02  to  0.10  per  cent),  sulphur  has  practically  no  effect  on  the 
strength  and  ductility  of  cold  steel,  but  it  does  have  an  injurious 
effect  on  the  properties  of  hot  steel.  It  causes  what  is  known  as 
"red  shortness"  (brittleness  at  a  red  heat)  and  makes  the  steel 
difficult  to  roll  and  weld.  Larger  amounts  of  sulphur  tend  to  de- 


232  MATERIALS  OF  CONSTRUCTION 

crease  the  strength  and  ductility.  The  sulphur  content  is  rarely 
over  0.06  per  cent  in  good  steel. 

Phosphorus. — In  small  amounts  phosphorus  increases  the 
strength  very  slightly,  but  it  is  a  very  undesirable  element  as  it 
makes  the  steel  very  brittle  and  unable  to  resist  shocks  or  blows. 
The  phosphorus  content  rarely  exceeds  0.07  per  cent  in  good 
steel. 

Manganese. — This  element,  in  small  amounts,  increases  the 
strength  slightly  and  the  hardness  and  malleability  to  a  greater  de- 
gree. The  effect  of  manganese  on  steel  increases  with  the  amount 
of  carbon  present,  and  it  has  a  greater  effect  on  acid  than  on 
basic  steel.  From  2.0  to  6.0  per  cent  of  manganese  makes  the 
steel  very  brittle.  The  amount  of  manganese  present  usually 
varies  from  0.04  to  1.1  per  cent,  depending  on 'the  kind  of  steel. 
Steel  containing  over  6.0  per  cent  of  manganese  is  called  man- 
ganese steel. 

313.  Effect  of  Mechanical  Working  and  Heat  Treatment— 
The  effect  of  mechanical  working  on  hot  steel  is  to  lessen  the 
effect  of  large  crystals,  flaws,  blowholes,  etc.,  and  to  increase  the 
solidarity,    specific    gravity,    and    strength.     If    the     finishing 
temperature  is  above  a  red  heat,  the  crystals  may  increase  in 
size   in    cooling   and   the   elastic   limit    and    ultimate  strength 
may  be  reduced.     However,  if  the  working  is  continued  so  that 
the  finishing  temperature  is  below  a  red  heat,  large  crystals  will 
be  unable  to  form  and  the  elastic  limit  and  ultimate  strength  will 
be  increased. 

Cold  working  may  be  done  on  soft  or  medium  steel,  but  not  on 
hard  steel  as  it  is  too  brittle.  The  effect  of  cold  working  is  to 
elongate  the  crystals,  decrease  the  ductility,  increase  the  brittle- 
ness,  raise  the  elastic  limit  considerably,  and  raise  the  ultimate 
strength  to  a  lesser  degree. 

Hardening  makes  the  steel  strong,  hard,  and  brittle,  while 
tempering  removes  some  of  the  brittleness  and  increases  the 
ductility  and  toughness  without  lessening  the  strength  very  much. 

In  general,  annealing  removes  the  effects  of  overstrain,  increases 
the  ductility,  and  lowers  the  strength.  The  effect  of  annealing 
depends  in  a  large  measure  on  the  annealing  temperature  and  the 
amount  of  carbon  in  the  steel. 

314.  Tensile  Strength  of  Steel. — The  elastic  limit  in  tension, 
which  is  about  50  or  60  per  cent  of  the  ultimate  strength,  varies 
from  about  25,000  to  120,000  Ib.  per  square  inch,  depending  on 


STEEL 


233 


the  kind  of  steel.  The  yield  point  is  usually  from  3,000  to 
5,000  Ib.  per  square  iach  more  than  the  elastic  limit.  The 
ultimate  strength  in  tension  varies  from  about  45,000  to  over 
200,000  Ib.  per  square  inch  according  to  the  kind  of  steel.  The 
modulus  of  elasticity  in  tension  is  about  29,000,000  or  30,000,000 
Ib.  per  square  inch,  and  is  practically  a  constant  for  all  kinds  of 
steel. 

The  ultimate  elongation  in  8  in.  usually  ranges  from  5  to  30 
per  cent,  and  the  reduction  in  area  from  10  to  60  per  cent. 


140,000 


160,000 


.100,000 


60,000 


•40,000 


20,000 


.15  .20 

Unit  Elongotion,  in.  per  in. 

FIG.  107. — Stress-strain    diagrams    for    carbon    steels  in  tension.      (Watertown 

Arsenal   Tests.) 


The  per  cent  elongation  and  the  per  cent  reduction  in  area 
decrease  as  the  strength  increases,  other  things  being  equal. 

The  fracture  of  steel  in  tension  is  usually  fine  and  silky  in 
appearance,  and  varies  from  a  full  cup  and  cone  for  soft  steel  to 
a  fracture  that  is  square  across  for  hard  steel. 

315.  Compressive  Strength  of  Steel. — The  elastic  limit  and 
modulus  of  elasticity  in  compression  are  practically  the  same  as  in 
tension.  Soft  and  medium  steels  have  no  ultimate  strength  in 
compression  as  the  metal  flows  and  flattens  out  as  the  load  is 
increased,  thus  increasing  the  cross  sectional  area.  The  ultimate 


234  MATERIALS  OF  CONSTRUCTION 

strength  for  structural  steel  is  usually  taken  as  60,000  Ib. 
per  square  inch. 

Hard  steel  has  a  definite  fracture  in  compression,  the  metal 
shearing  off  at  an  angle  with  the  load  axis.  Sometimes  the 
specimen  breaks  in  many  pieces.  The  strength  in  compression 
for  hard  steel  is  from  10  to  25  per  cent  greater  than  that  in 
tension. 

The  tensile  and  compressive  properties  of  steel  are  very  closely 
related,  and  the  two  stress  strain  curves  are  very  much  alike  in 
appearance. 

316.  Shearing  Strength  of  Steel. — In  shear,  the  values  of  the 
elastic  limit  and  ultimate  strength  are  about  70  or  80  per  cent 
of  those  in  tension  for  the  same  kind  of  steel.     The  shearing 
modulus  of   elasticity  is  about  12,000,000  Ib.  per  square  inch 
for  all  kinds  of  steel. 

The  computed  shearing  stress  in  torsion  at  the  ultimate 
(torsional  modulus  of  rupture)  gives  values  that  are  about  one- 
third  higher  than  those  obtained  in  direct  shear.  The  reason 
for  this  is  that  the  formula  for  torsional  stress  does  not  consider 
the  decrease  in  the  shearing  modulus  of  elasticity  after  the 
elastic  limit  has  been  passed. 

317.  Transverse     Strength     of     Steel. — The     cross-bending 
strength  of  steel  depends  upon  its  strength  in  tension  and  com- 
pression.    The  failure  will  be  either  in  tension  or  compression, 
depending  on  the  form  of  the  beam  and  the  position  of  the 
neutral  axis.     Other  things  being  equal,  the  softer  steels  will 
usually  fail  first  in  compression,  while  the  harder  steels  will  fail 
in  tension.     The  elastic  limit  and  modulus  of  elasticity  have  the 
same  values  in  cross  bending  as  in  tension,  while  the  ultimate  is 
the  same  as  that  in  tension  or  compression,  depending  on  the 
kind  of  failure. 

The  deflection,  up  to  the  elastic  limit,  depends  on  the  manner 
of  loading,  kind  of  supports,  length  of  span,  and  the  moment  of 
inertia  of  the  cross  section  (the  modulus  of  elasticity  being  con- 
sidered a  constant  for  all  steels).  The  maximum  deflection  at 
the  time  of  failure  is  also  dependent  on  the  yield  point  and  the 
ductility  of  the  steel. 

318.  Average    Properties    of    Rolled    Carbon    Steels.— The 
following  table  gives  average  properties  of  various  rolled  carbon 
steels.     All  stresses  are  in  pounds  per  square  inch,  and  elongations 
and  reductions  of  areas  are  in  percentages. 


STEEL  235 

AVERAGE  PROPERTIES  OF  VARIOUS  ROLLED  CARBON  STEELS 


Per  cent  of  carbon 

Elastic  limit,  tension  and  com- 
pression   

Elastic  limit,  shear 

Ultimate  strength,  tension 

Ultimate  strength,  compression . .  . 

Ultimate  strength,  shear 

Modulus  of  rupture,  cross  bending. 

Modulus  of  elasticity,  tension, 
compression,  and  cross  bending. 

Modulus  of  elasticity,  shear 

Per  cent  elongation  in  2  in 

Per  cent  elongation  in  8  in 

Per  cent  reduction  in  area  (tension) 


0.10 

30,000 
18,000 
50,000 
(50,000) 
35,000 
50,000 


0.20 

35,000 
21,000 
60,000 
(60,000) 
45,000 
60,000 


0.40 

50,000 
30,000 
90,000 
105,000 
65,000 
95,000 


0.60 


60,000 
36,000 


70,000 


42,000 


115,000135, 
135,000,155,000 
85,000  100,000 
125,000|145,000 


1.00 


29,000,000  to  30,000,000 
About  12,000,000 


u 

25 

.-,0 


80,000 
48,000 
000  150,000 
175,000 
115,000 
160,000 


Hard  steels,  which  have  been  subjected  to  heat  treatment,  will 
probably  have  greater  strength  and  less  ductility  than  rolled  hard 
steels.  The  process  of  manufacture,  methods  of  treatment  in 
rolling,  and  the  presence  of  various  chemical  elements  all  have 
some  influence  on  the  strength  and  properties.  Therefore, 
results  from  any  individual  test  may  differ  considerably  from  the 
average  values  given  in  the  table. 

319.  Effect   of   Combined    Stresses. — In   general,    combined 
stresses  tend  to  lower  the  elastic  limit  and  ultimate  strength  in 
either  kind  of  stress.     Torsional  stress  will  lower  the  elastic 
limit  and  ultimate  strength  in  tension,  compression,  and  cross 
bending,  the  amount  of  lowering  being  dependent  on  the  amount 
of   torsional   stress   present.     Similarly,    the   elastic   limit   and 
ultimate  in  shear  are  lowered  by  the  existence  of  any  of  the 
other  stresses,  depending  upon  their  amount.     This  decrease  or 
lowering  of  strength  under  any  one  kind  of  stress  in  combined 
stresses  may  be  from  10  to  80  per  cent,  depending  on  the  amount 
and  kind  of  the  other  stress  or  stresses  present. 

320.  Resistance  to  Impact  Loads. — The  resistance  of  steel  to 
impact  is  of  importance  because  steels  are  often  subjected  to 
blows  and  sudden  loads  in  structural  and  other  work.     There 
is  no  generally  accepted  method  for  making  impact  tests;  the 
test  most  commonly  used  being  a  drop  test  in  which  a  given 
weight  is  dropped  from  a  given  height  on  a  specimen  of  a  certain 
size  supported  over  a  definite  span  on  a  heavy  anvil  block. 
Probably  the  best  method  of  measuring  the  resistance  of  steel  to 
impact  is  to  determine  the  amount  of  work  in  impact  required 
to  deform  a  unit  volume  of  the  steel  to  rupture.     This  unit  may 
be  expressed  in  inch  pounds  per  cubic  inch  or  in  foot-pounds 


236 


MATERIALS  OF  CONSTRUCTION 


per  cubic  inch.  In  a  static  test,  the  work  required  to  deform 
the  specimen  to  rupture  is  equal  to  the  area  under  the  stress 
strain  curve.  The  values  obtained  from  impact  tests  are  usually 
from  20  to  30  per  cent  higher  than  those  obtained  from  static 
tests. 

The  following  table  gives  the  results  from  some  experiments 
made  by  Professor  Hatt  of  Purdue  University.  The  static  tests 
were  tensile  tests. 


Material 

Tensile 
strength, 
pounds  per 
square  inch 

Work  of  rupture  in  foot- 
pounds per  cubic  inch 

Static 

Impact 

Soft  steel  

63,000 
80,000 
62,000 
85,000 
140,000 
83,000 
109,000 

1,376 
1,230 
1,450 
1,414 
976 
566 
348 

1,358 
1,855 
2,315 
1,821 
2,918 
544 
626 

Boiler  steel 

Soft  steel  casting 

Nickel  steel  

Locomotive-tire  steel  
Annealed  wire  
Steel  wire  

321.  Ductility  of  Steel.— The  ductility  of  steel  may  be 
measured  by  the  elongation  and  reduction  in  area  in  a  tension 
test  (see  Art.  318  for  average  values  for  rolled  carbon  steels). 

The  ductility  of  steel  is  often  measured  by  a  cold-bending  test, 
which  consists  of  bending  a  specimen  over  a  sharp  edge  or  about 
a  pin  or  template  of  a  certain  radius.  Cold  bending  may  be 
done  in  a  vise,  on  an  anvil,  or  by  the  use  of  a  steam  hammer  or  a 
hydraulic  press.  Testing  machines  have  been  made  especially 
for  this  test.  The  cold  steel  should  be  able  to  bend  around  a 
certain  pin  through  an  angle  of  the  required  number  of  degrees 
without  cracking.  The  following  table  gives  the  values  that 
ordinary  carbon  steel  should  bend  without  cracking. 

COLD-BENDING  TEST  OF  STEEL, 


Kind  of  steel 

Degrees  of  bend 

Diameter  of  pin 

Low-carbon  steel 

180 

Zero 

Medium-carbon  steel  

180 

2  X  the  thickness  of  steel 

High-carbon  steel  
Very  high-carbon  steel          .    . 

90 
60 

3  X  the  thickness  of  steel 
3  X  the  thickness  of  steel 

STEEL  237 

322.  Hardness  of  Steel. — Hardness  may  be  said  to  mean  any 
one  of  many  things  such  as  the  ability  of  a  tool  to  keep  its  cutting 
edge,  the  resistance  of  wheels  and  rails  to  wear  due  to  rolling 
friction,  resistance  to  abrasion,  resistance  to  indentation,  etc. 
There  are  many  ways  of  measuring  the  hardness  of  steels,  but 
only  a  few  of  the  most  common  ones  will  be  mentioned. 

The  Brinell  method  determines  the  resistance  to  indentation 
by  measuring  the  indentation  of  a  hardened  sphere  of  a  given  size 
and  under  a  given  pressure.  Results  of  tests  made  with  a 
Brinell  machine  tend  to  show  that  the  hardness  of  steel  is  directly 
proportional  to  its  tensile  strength.  The  Brinell  method  seems 
to  be  the  best  test  yet  proposed. 

In  the  Shore  scleroscope  test,  the  hardness  is  determined  by 
measuring  the  rebound  of  a  pointed  hammer  that  falls  upon 
the  metal  from -a  definite  height  through  a  guiding  glass  tube. 
This  method  seems  to  give  parallel  results  with  the  Brinell 
method. 

In  the  Bauer  drill  test,  a  special  drill  is  driven  at  constant 
speed  under  a  fixed  pressure.  The  hardness  is  measured  by  the 
depth  of  hole  drilled  in  a  given  number  of  revolutions.  The 
softer  the  steel,  the  deeper  the  hole. 

323.  Effect  of  Repeated  and  Alternating  Stresses. — It  has 
been  found  that  a  stress  which  is  often  repeated  or  alternated  in  a 
steel  bar  will  finally  cause  a  molecular  change  in  the  steel  which 
lowers  its  strength  and  which  may  result  in  rupture  of  the  bar. 
The  repeated   or  alternating   stress  tends  to  break  down  the 
structure  of  the  individual  crystals  and  to  cause  them  to  fail  by 
shear   slips.     This  loss  of  strength  is  called  " fatigue"  of  the 
steel. 

The  average  stress  causing  the  rupture  of  a  steel  bar  depends 
upon  the  maximum  stress  applied  to  the  extreme  crystals,  the 
behavior  of  these  crystals,  and  the  effect  of  the  failure  of  a  few 
crystals  on  the  others.  Small  crystals  resist  repeated  stresses 
better  than  large  crystals  do. 

Results  of  tests  have  shown  that  steel  may  be  ruptured  by 
repeated  applications  of  a  stress  much  less  than  the  ultimate, 
and  that  the  number  of  repetitions  required  for  failure  increases, 
very  rapidly  as  the  stress  decreases.  If  the  maximum  stress 
is  greater  than  the  elastic  limit,  failure  may  occur  after  a  compara- 
tively few  applications;  but  if  the  stress  is  much  less  than  the 
elastic  limit,  an  enormous  number  (millions)  of  repetitions  will 


238  MATERIALS  OF  CONSTRUCTION 

be  required  to  cause  failure.  In  general,  the  resistance  of 
high-carbon  steels  to  repeated  stresses  appears  to  be  greater  than 
that  of  low-carbon  steels. 

324.  Welding  of  Steel. — Soft   steel   is   quite   easy   to   weld, 
medium  steel  is  weldable,  hard  steel  is  very  difficult  to  weld,  and 
it  is  practically  impossible  to  weld  very  hard  steel.     In  soft 
steel  the  efficiency  of  the  welded  joint  rarely  exceeds  70  per  cent, 
while  in  medium  steel  the  efficiency  is  rarely  over  55  per  cent, 
even  though  the  welding  is  done  by  expert  workmen. 

The  thermit  process  for  welding  fractures  in  wrought  iron  and 
steel  depends  on  the  affinity  of  powdered  aluminum  for  iron 
oxide.  If  these  two  substances  are  finely  mixed  and  ignited,  the 
resulting  chemical  action  will  raise  the  temperature  of  the  adjacent 
metal  to  about  5,400  degrees  Fahrenheit,  which  is  high  enough  to 
allow  of  the  melting  and  welding  of  any  ordinary  casting  or  forging. 
This  process  is  much  used  for  repairing  breaks  in  large  castings. 

If  acetylene  gas  and  oxygen  are  properly  mixed  and  ignited,  they 
will  generate  a  temperature  of  about  6,000  degress  Fahrenheit 
which  may  be  used  to  weld  or  fuse  metals.  The  oxygen-acetylene 
process  is  much  used  for  cutting  metals. 

In  electric  welding,  an  alternating-current  dynamo  of  fairly 
high  voltage  is  connected  to  a  transformer  whose  secondary 
terminals  give  an  electric  current  of  large  amperage  and  very  low 
voltage  (about  3  volts) .  These  secondary  terminals  are  connected 
to  the  welding  clamps.  The  flow  of  a  large  current  through  the 
resistance  offered  by  the  two  pieces  of  steel  where  they  are  in 
contact  with  each  other  causes  the  contact  surfaces  to  be  heated 
hot  enough  to  weld  or  fuse  together. 

325.  Magnetic  Properties  of  Steel. — The  magnetic  properties 
of  steel  depend  to  a  large  extent  on  its  composition,  mechanical 
working,  and  heat  treatment. 

The  carbon  content  should  be  low,  less  than  0.1  per  cent. 

Silicon  decreases  the  hysteresis  loss,  increases  the  resistivity, 
reduces  eddy  currents,  increases  the  permeability  in  a  weak  field, 
and  decreases  the  permeability  in  a  strong  field. 

More  than  0.3  per  cent  of  manganese  appears  to  have  a  bad 
effect  on  the  magnetic  properties. 

Sulphur  and  phosphorus  have  a  bad  effect  on  the  magnetic 
properties  of  steel.  The  total  sulphur  and  phosphorus  content 
should  be  less  than  0. 1 5  per  cent,  and  there  should  not  be  more  than 
0.10  per  cent  of  either  sulphur  or  phosphorus. 


STEEL  239 

In  general,  hot  steel  (between  300  and  600  degrees  Centigrade) 
has  a  slightly  greater  intensity  of  induced  magnetism  than  cold 
steel.  At  about  200  degrees  Centigrade,  there  seems  to  be  a 
characteristic  decrease  in  the  intensity.  Also,  as  the  steel 
approaches  closer  to  the  critical  point  (700  to  800  degrees 
Centigrade)  in  temperature,  the  intensity  decreases  and  becomes 
practically  zero  when  the  critical  point  is  reached. 

Cold  working  of  steel  appears  to  be  somewhat  injurious  to  the 
magnetism,  but  proper  annealing  seems  to  remove  most  of  the 
bad  effects.  Annealing  makes  the  steel  softer  and  weaker  and 
increases  the  magnetic  properties.  Hardening  by  quenching  in 
oil  or  water  has  a  bad  effect  on  the  magnetic  properties.  Temper- 
ing after  hardening  has  a  good  effect  in  many  cases. 

In  general,  the  weaker  and  softer  a  steel  is,  the  more  magnetic 
it  is. 

326.  Specific  Gravity  and  Coefficient  of  Expansion  of  Steel.— 
The  specific  gravity  of  steel  is  about  7.8,  and  the  weight  is  about 
490  Ib.  per  cubic  foot.     Thorough  mechanical  working  tends  to 
increase  slightly  the  specific  gravity  and  weight  per  cubic  foot. 

The  coefficient  of  expansion  of  steel  is  approximately  0.0000065 
per  degree  Fahrenheit. 

327.  Summarized    Specifications    for    Various   Steels. — The 
following  table  gives  the  summarized  requirements  or  specifications 
for  various  steels.     Most  of  the  values  have  been  taken  from  the 
1916  "Book  of  Standard  Specifications  of  the  American  Society 
for  Testing  Materials."     With  some  exceptions,  the  open-hearth 
process  of  manufacture  is  required.     The  nickel   steel  in  the 
table  should  contain  3.25  per  cent  or  more  of  nickel. 


240  MATERIALS  OF  CONSTRUCTION 

MINIMUM  REQUIREMENTS  FOR  VARIOUS  STEELS 


Elongation  in 

Elastic 

Ultimate 

Carbon, 

limit, 

tensile 

Cold- 

Use 

per  cent 

pounds  per 

strength, 

bend 

square  inch 

pounds  per 

8  in. 

2  in. 

test 

square  inch 

Structural-rivet  steel  

0.08  to  0.15 

30,000 

55  ,  000 

30 

Yes 

Structural  steel  

0.18  to  0.30 

35,000 

60  ,  000 

25 

Yes 

Boiler-rivet  steel  

0.  08  to  0.  15 

25,000 

50,000 

30 

Yes 

Boiler-plate  steel  

0.08  to  0.15 

30,000 

60,000 

27 

Yes 

Boiler-flange  steel  

0.  12  to  0.25 

30  ,  000 

60  ,  000 

25 

Yes 

Boiler-firebox  steel  

0.12  to  0.25 

28  ,  000 

57  ,  000 

27 

Yes 

Structural  nickel  steel  

0.  20  to  0.  45 

52  ,  000 

95  ,  000 

20 

Yes 

Nickel  steel  for  rivets  

0.  15  to  0.  30 

45  ,  000 

75  ,  000 

20 

Yes 

Reinforced  concrete  bars.  . 

0.  20  to  0.  40 

40,000 

70,000 

20 

Yes 

(Rerolled  from  rails)  .... 

0.  20  to  0.  50 

50  ,  000 

80  ,  000 

15 

Yes 

Mild  forge  steel 

0.  10  to  0.  20 

30  ,  000 

55  ,  000 

25 

No 

Medium  forge  steel  

0.20  to  0.40 

40  ,  000 

75  ,  000 

20 

No 

Heat-treated  forge  steel  .  .  . 

0.  15  to  0.40 

65  ,  000 

110,000 

20 

No    . 

Machinery  steel  

0.  35  to  0.  60 

40,000 

75  ,  000 

20 

Rail  steel  

0.  35  to  0.  55 

45  ,  000 

80,000 

18 

Yes 

Steel  railway  tires  

0.  50  to  0.  85 

60  ,  000 

115,000 

10 

No 

Axle  steel 

0.  35  to  0.  55 

55  ,  000 

100,000 

15 

18 

Yes 

Gun  steel.  . 

0.  20  to  0.  50 

50  ,  000 

90  ,  000 

16 

Yes 

Spring  steel  

1.00  to  1.50 

60  .  000 

125.000 

12 

Yes 

Tool  steel  

0.90  to  1.  50 

80,000 

150,000             8 

No 

Cable-  wire  steel  

0.70  to  1.50 

100,000 

200,000 

6 

328.  Working  Stresses  for  Structural  Steel.— The  allowable 
unit  working  stresses  for  steel  depend  on  the  kind  of  steel  and  the 
kind  of  loading.  The  working  unit  stress  should  never  exceed 
the  elastic  limit  of  the  steel.  Often  the  allowable  working  unit 
stress  for  variable  loads  is  taken  at  about  half  of  the  elastic  limit. 
This  value  may  be  increased  about  33  per  cent  for  steady  stresses; 
decreased  about  30  or  40  per  cent  for  repeated  or  alternating 
stresses;  and  decreased  about  50  per  cent  for  impact,  shocks,  or 
sudden  loads.  A  simple  rule  for  determining  the  allowable  unit 
stress  for  varying  loads  is:  Add  to  the  maximum  load  the  dif- 
ference between  the  maximum  and  minimum  loads  and  treat  the 
sum  as  a  static  load.  Then  use  the  allowable  working  unit 
stress  for  steady  stresses  and  design  accordingly. 

The  following  table  gives  average  values  of  working  unit 
stresses  for  structural  steel  under  various  loads: 


STEEL 


241 


AVERAGE  VALUES  OF  ALLOWABLE  WORKING  UNIT  STRESSES  FOR 
ORDINARY  STRUCTURAL  STEEL 


Stress 

Material 

Unit  working  stress  in  pounds  per 
square  inch 

Variable 

Steady 

Alter- 
nating 

Impact 

Tension  

Medium  rolled  or  cast  steel  
Medium  rolled  or  cast  steel  

Rolled  beams  and  riveted  beams  .  . 
Rolled  pins,  rivets,  and  bolts  
Steel  web  plates,  shop  rivets,  and 
pins  

16,000 
16,000 

16,000 
20,000 

10,000 
9,000 
8,000 
20,000 
18,000 

21,000 
21,000 

21,000 
26,000 

13,000 
12,000 
11,000 
26,000 
24,000 

10,000 
10,000 

10,000 
13,000 

6,500 
6,000 
5,000 
13,000 
12,000 

8,000 
8,000 

8,000 
10,000 

5,000 
4,500 
4,000 
10,000 
9,000 

Compression 
(short  blocks) 
Bending  
Bending  
Shear       

Shear 

Shear 

Field  bolts 

Bearing  
Bearing  

Shop  rivets  and  pins  

Field  rivets 

' 

329.  Uses  of  Steel. — Steel  is  probably  the  most  important 
structural  material  in  the  world  at  the  present  time  and  its  uses 
are  practically  innumerable.  Some  of  its  more  important  uses 
are:  structural  steel  for  buildings,  ships,  bridges,  viaducts,  and 
trestles;  steel  machinery  of  all  kinds;  railroad  locomotives 
and  cars;  street  railway  cars;  automobiles  and  wagons;  dynamos, 
motors,  and  other  electrical  machinery;  standpipes  and  tanks; 
hydraulic  machinery;  steel  boilers  and  engines;  guns,  armor,  and 
projectiles;  tools,  saws,  lathes,  planers,  millers,  and  all  kinds  of 
metal  and  wood  working  machinery ;  cutlery,  surgical  instruments, 
and  delicate  apparatus  of  all  kinds;  wire;  concrete  reinforcement; 
etc. 

The  following  are  the  uses  of  various  carbon  steels.  The  uses 
of  the  special  and  alloy  steels  will  be  given  in  the  articles  describ- 
ing those  steels. 

USES  OF  VARIOUS  CARBON  STEELS 

Carbon  0.05  to  0.15  per  cent 

Electrical  sheet  steel;  boiler  plate;  rivets;  bolts;  stock  for  case 
hardening;  nails;  ship  plate;  forge  work;  sheet  steel  for  tinning 
and  galvanizing. 

Carbon  0.15  to  0.25  per  cent 

General  structural  steel  for  bridges,  buildings,  etc.;  forge 
steel;  flange  and  firebox  steel;  ship  plate;  rivets;  cold-rolled 
shafting. 

16 


242  MATERIALS  OF  CONSTRUCTION 

Carbon  0.25  to  0.40  per  cent 

Machine  parts  in  general;  axles;  shafts;  connecting  rods; 
piston  rods;  steel  castings;  reinforced  concrete  bars;  medium 
forge  steel. 

Carbon  0.40  to  0.75  per  cent 

Railroad  rails;  steel  castings;  machinery  steel;  steel  railway 
tires. 

Carbon  0.60  to  0.80  per  cent 

Steel  railway  tires;  hammers;  cutlery;  wood  working  tools; 
small  lathe  tools;  small  dies;  cold  sets;  drills;  taps;  reamers;  cold 
chisels;  wire. 

Carbon  0.80  to  1.00  per  cent 

Carbon  steel  springs;  ordinary  lathe  tools;  large  dies,  drills,  and 
chisels;  steel  wire  and  cable. 

Carbon  1.00  to  1.20  per  cent 

Large  lathe  tools;  large  and  carefully  heat-treated  dies  and 
drills;  axes;  hatchets;  knives;  spring  steel;  cable-wire  steel. 

Carbon  1.20  to  1.50  per  cent 

Some  tool  steels;  spring  steels;  saws;  files;  jeweler's  dies;  balls 
and  ball  bearings. 


CHAPTER  XIV 

SPECIAL  STEELS  AND  CORROSION  OF  IRON  AND  STEEL 

A.  STEEL  CASTINGS 

330.  Definition  and  Uses  of  Steel  Castings. — Steel  castings 
are   unforged   or   unrolled   castings   made   of   bessemer,    open- 
hearth,  crucible,  or  any  other  kind  of  steel. 

Steel  castings  are  used  in  many  places  in  preference  to  cast 
iron,  and  are  often  cheaper  than  built-up  sections  of  structural 
steel.  Some  of  the  uses  of  steel  castings  are:  bedplates,  stern 
posts,  stems,  hydraulic  cylinders,  shaft  struts,  hawse  pipes, 
stern  pipes,  crossing  frogs,  parts  of  railway  cars,  pinions,  gears, 
hammer  dies,  gun  carriages,  various  machine  parts,  etc. 

331.  Founding  of  Steel  Castings. — In  general,  the  founding  of 
steel  castings  is  the  same  as  that  for  cast  iron,  except  that  much 
greater  care  must  be  used  throughout. 

The  proper  design  of  the  patterns  and  cores  is  very  important 
in  steel  castings.  Intricate  castings  must  be  designed  so  that 
they  will  cool  uniformly,  or  severe  internal  stresses  or  cracks 
will  be  formed.  A  large  shrinkage  must  be  allowed  for,  varying 
from  %Q  to  J4  m-  Per  foot.  An  uneven  shrinkage  is  bad. 

A  special  molding  sand,  consisting  essentially  of  certain  kinds 
of  silica  sand,  must  be  used  to  prevent  the  steel  from  sticking  to 
the  molding  material. 

The  molten  steel  used  should  have  the  proper  chemical  pro- 
portions to  give  good  castings.  Sufficient  quantities  of  silicon 
and  manganese  should  be  present  to  eliminate  blowholes  and 
flaws,  and  to  aid  in  the  solidifying  of  the  steel,  though  large 
quantities  of  these  elements  will  cause  brittleness.  It  is  better 
to  pour  the  metal  very  hot,  as  it  makes  smoother  castings,  and 
make  allowance  for  the  increased  shrinkage.  The  castings  are 
removed  from  the  molds  and  cleaned  in  the  same  manner  as 
iron  castings. 

Annealing  a  steel  casting  reduces  the  effect  of  overstrains 
caused  by  shrinkage  and  uneven  cooling,  has  but  little  effect  on 
the  tensile  strength,  and  increases  the  ductility,  especially  of 
medium  and  hard  castings. 

243 


244 


MATERIALS  OF  CONSTRUCTION 


332.  Properties  of  Steel  Castings.— The  physical  qualities  of 
soft,  medium,  and  hard  steel  castings  are  about  the  same  as  the 
physical  qualities  of  soft,  medium,  and  hard  steel,  except  that 
the  elastic  limit,  elongation,  and  reduction  of  area  are  a  little 
less.  The  effect  of  various  chemical  elements,  heat  treatments, 
etc.  is  the  same  on  steel  castings  as  on  the  ordinary  steels.  The 
chemical  elements  and  treatments  can  be  controlled  so  as  to 
produce  the  steel  castings  that  are  the  most  suitable  for  the 
given  purpose. 

Good  steel  castings  should  rarely  contain  over  0.40  per  cent 
of  carbon,  unless  it  is  desired  to  secure  a  hard,  strong  casting 
that  will  resist  wear.  The  phosphorus  should  be  less  than  0.07 
per  cent,  and  the  sulphur  less  than  0.05  per  cent. 

The  following  table  gives  the  minimum  requirements  for  the 
strength  and  ductility  of  steel  castings  as  specified  by  the 
American  Society  for  Testing  Materials : 

MINIMUM  REQUIREMENTS  FOR  STEEL  CASTINGS 


Physical  quality 

Soft 
castings 

Medium 
castings 

Hard 

castings 

Ultimate  tensile  strength,  Ib. 
per  square  inch  
Yield  point  in  tension,  Ib.  per 
square   inch 

60,000 
27  ,  000 

70,000 
31  500 

85,000 
38  250 

Per  cent  elongation  in  2  in  ... 
Per  cent  reduction  of  area  .... 
Cold-bending  test  

22 
30 
Yes 

18 
25 
Yes 

15 
20 
No 

B.  ALLOY  STEELS 

333.  Definition  and  Classification  of  Alloy  Steels.— Alloy 
steels  are  those  steels  which  owe  their  distinctive  properties 
chiefly  to  the  presence  of  an  element  or  elements  other  than 
carbon,  or  jointly  to  the  presence  of  some  such  element  or 
elements  and  carbon. 

Alloy  steels  are  usually  classified  according  to  the  presence  of 
one  or  more  principal  elements  besides  carbon.  Three  part 
alloys  are  those  whose  properties  are  chiefly  dependent  on  one 
other  element  besides  carbon  and  iron;  4  part  alloys  contain  two 
other  such  chief  elements;  and  5  part  alloys  have  three  other 


SPECIAL  STEELS  AND  CORROSION  OF  IRON  AND  STEEL    245 

such  elements.  Tungsten  steel,  chromium-nickel  steel,  and 
chromium-nickel-vanadium  steel  are  examples  of  3,  4,  and  5  part 
alloys  respectively. 

The  names  given  to  the  various  alloy  steels  indicate  the  names 
of  the  alloying  elements  present. 

Only  a  brief  summary  of  the  properties  and  uses  of  some  of  the 
most  important  alloy  steels  will  be  given  in  the  following 
paragraphs. 

334.  Heat  Treatment  of  Alloy  Steels.— The  proper  heat 
treatment  of  alloy  steels  is  very  important  as  it  materially  affects 
the  strength  and  other  properties.  In  the  heat  treatment  the 
following  things  should  be  considered:  the  original  chemical 
and  physical  properties  of  the  metal;  the  composition  of  the  gases 
and  other  substances  that  come  in  contact  with  the  metal  during 
the  heating  and  cooling;  the  rate  of  increase  of  temperature;  the 
maximum  temperature  reached ;  the  length  of  time  that  the  metal 
is  kept  at  this  temperature;  and  the  rate  of  cooling. 

In  general,  the  heat  treatment  of  alloy  steels  is  easier  to  control 
than  that  of  ordinary  carbon  steels  because:  (1)  in  many  cases 
the  critical  temperatures  are  lower,  and,  consequently,  the 
changes  in  structure  at  the  critical  temperatures  are  slower  and 
more  easily  controlled;  and  (2)  the  substances  in  solution  in  the 
various  forms  of  iron  appear  to  retard  and  slow  up  the  rate  of 
change  from  one  form  to  another. 

Some  elements,  such  as  manganese  and  nickel,  lower  the  critical 
temperatures.  Other  elements,  such  as  chromium,  lower  the 
critical  temperatures  and  also  form  special  carbides;  while  some 
elements,  of  which  tungsten,  vanadium,  molybdenum  and 
probably  aluminum,  copper,  and  titanium  are  examples,  form 
special  carbides  and  only  slightly  lower  the  critical  temperatures. 
Silicon  acts  in  about  the  same  way  as  carbon,  and  has  practically 
no  effect  on  the  critical  temperature.  If  a  sufficient  amount  of 
silicon  is  present,  it  will  throw  the  carbon  out  of  solution  as  graph- 
ite and  thus  cause  the  steel  to  be  too  brittle  for  engineering  use. 

Frequently,  a  double  quenching  of  an  alloy  steel  gives  very 
good  results.  The  metal  is  first  quenched  to  a  certain  temper- 
ature in  one  bath  (such  as  a  lead  bath  heated  to  the  proper 
temperature)  and  then  quenched  again  and  completely  cooled 
by  being  immersed  in  a  second  bath.  Sometimes  the  metal  is 
allowed  to  cool  slowly  in  air  after  the  first  quenching. 

In  general,  a  high-grade  alloy  steel  should  be  annealed  after 


246  MATERIALS  OF  CONSTRUCTION 

every  process  in  the  manufacturing,  such  as  forging,  pressing, 
rolling,  rough  machining,  etc.  The  metal  should  also  be  annealed 
before  hardening  or  case  hardening. 

335.  Nickel  Steel. — Nickel  steel  usually  contains  from  2.75  to 
4.5  per  cent  of  nickel  and  from  0.20  to  0.40  per  cent  of  carbon. 
It  combines  hardness,  great   tensile  strength,  and  high  elastic 
limit  with  great  ductility.     The  specific  gravity  is   about    the 
same  as  that  of  carbon  steels,   and  increases  slightly  with  an 
increase  of  nickel.     The  resistance  to  corrosion  increases  with 
increase  of  nickel  up  to  about  18  per  cent  of  nickel.     Ordinary 
nickel  steel,  containing  about  3.5  per  cent  of  nickel,   corrodes 
slightly  less  than  carbon  steel.     Nickel  steel  has  a  high  electrical 
resistance.     Ordinary    nickel    steel    possesses    a  magnetic  per- 
meability greater  than  wrought  iron. 

An  addition  of  about  3.5  per  cent  of  nickel  to  a  medium  carbon 
steel  raises  the  elastic  limit  and  ultimate  about  50  per  cent  and 
increases  the  elongation  about  15  per  cent.  Nickel  steel  has 
been  made  with  elastic  limits  varying  from  48,000  to  120,000  Ib. 
per  square  inch;  with  ultimates  varying  from  90,000  to  277,000 
Ib.  per  square  inch;  and  with  elongations  varying  from  25  to  3 
per  cent  in  tension.  Ordinary  nickel  steel  rarely  receives  a  heat 
treatment. 

Nickel  steel  is  used  for  guns,  armor  plate,  structural  steel, 
rivets,  railroad  steel,  machine  parts,  axles,  shafts,  etc.  Invar  is  a 
nickel  steel  (containing  about  36  per  cent  of  nickel)  with  a  low- 
expansion  coefficient. 

336.  Manganese    Steel.— Manganese    steel   usually    contains 
from  6  to  20  per  cent  of  manganese  with  less  than  1.5  per  cent  of 
carbon.     The  composition  for  the  best  results  is  about  as  follows: 
12  to  15  per  cent  of  manganese,  less  than  0.6  per  cent  of  carbon, 
less  than  0.4  per  cent  of  sulphur,  and  less  than  0.4  per  cent  of 
phosphorus.     Manganese  steel  is  strong,  hard,  tough,  and  malle- 
able, and  offers  a  high  resistance  to  wear.     This  steel  is  usually 
cast  to  form,  but  can  be  hot  worked  at  a  yellow  heat.     It  is 
softened  by  quenching  from  a  yellow  heat,  and  hardened  by 
very    slow    cooling   from    high    temperatures.     Strength       and 
ductility  increase  with  manganese  up  to  about  15  per  cent,  after 
which  they  decrease.     The  maximum  tensile  strength  is  more 
than  140,000  Ib.  per  square  inch,  and  the  elastic  limit  more  than 
90,000  Ib.  per  square  inch.     The  maximum  elongation  is  more 
than  40  per  cent  in  2  in.,  and  the  maximum  reduction  in  area  is 


SPECIAL  STEELS  AND  CORROSION  OF  IRON  AND  STEEL    247 

over  50  per  cent.     The  shrinkage  of  manganese  steel  is  more  than 
that  of  ordinary  steel. 

Manganese  steel  is  used  where  hardness,  toughness,  strength, 
and  malleability  are  desired  as  for  rails,  frogs,  crossings,  car 
wheels,  axles,  tires,  and  for  parts  of  crushing,  rolling,  and  grinding 
machinery. 

337.  Vanadium  Steel. — Vanadium  steel  contains  from  0.1  to 
0.6  per  cent  of  vanadium.     This  element  gives  the  steel  a  very 
high  elastic  limit  and  ultimate  strength  without  decreasing  the 
ductility.     This  steel  is  also  very  tough  and  able  to  resist  impact 
stresses  when  properly  made.     The  maximum  ultimate  tensile 
strength  varies  from  60,000  to  180,000  Ib.  per  square  inch,  and 
the  elongation  from  40  to  20  per  cent,  depending  on  the  heat 
treatments    and    amounts   of   vanadium    and    carbon    present. 

Vanadium  steel  is  used  in  many  places  where  a  high  elastic 
limit  and  ultimate  strength  combined  with  a  large  shock  resist- 
ance is  desired,  as  in  springs,  axles,  shafts,  gears,  parts  of 
railroad  rolling  stock  and  automobiles,  etc. 

338.  Chrome  Steel. — Chrome  steel  contains  from  1.0  to  2.5 
per  cent  of  chromium  with  from  0.8  to  2.0  per  cent  of  carbon. 
The  chromium  increases  the  elastic  limit,  ultimate  strength,  and 
hardness.     Chrome  steel  is  used  to  some  extent  for  cutlery  as  the 
chromium  tends  to  make  the  steel  rust  proof.     Though  chrome 
steel  has  been  used  a  little  for  structural  work,  it  is  rarely  used 
now  because  of  the  discovery  of  better  and  cheaper  alloy  steels. 

339.  Silicon  and  Aluminum  Steels. — Silicon  steel  resembles 
nickel  steel  in  its  properties,  and  is  used  mostly  for  the  cores, 
pole  pieces,  etc.  of  electrical  machinery.     Silicon,  up  to  about 
4  per  cent,  increases  the  elastic  limit  and  ultimate,  after  which 
there   is   a   decrease.     The   ductility   decreases   as   the   silicon 
increases.     For  electrical  work,  about  3  per  cent  of  silicon,  with 
low  percentages  of  the  other  elements,  seems  to  give  the  best 
results. 

Aluminum  steel  is  no  harder  or  stronger  than  ordinary  steel, 
but  it  is  more  solid  and  has  less  blowholes.  Aluminum  tends  to 
cause  hot  and  cold  shortness.  The  effect  of  aluminum  is  about 
the  same  as  silicon;  consequently,  aluminum  is  rarely  used  as 
the  silicon  is  much  cheaper. 

340.  Tungsten,  Molybdenum,  and  Cobalt  Steels. — Tungsten 
steel  contains  from  3.0  to  5.0  per  cent  of  tungsten  together 
with  a  little  chromium  and  manganese.     The  tensile  properties 


248  MATERIALS  OF  CONSTRUCTION 

resemble  those  of  high-carbon  steel,  the  ultimate  strength  and 
elastic  limit  being  high,  the  ductility  low,  and  the  hardness 
quite  great.  This  steel  is  used  for  tools  in  metal  cutting,  and 
some  grades  will  cut  when  red  hot.  Tungsten  is  a  hardener  of 
steel. 

Molybdenum  steel  contains  from  0.3  to  3.0  per  cent  of 
molybdenum.  This  steel  is  similar  to  tungsten  steel  in  its 
properties,  1  per  cent  of  molybdenum  having  about  the  same 
effect  as  2  or  3  per  cent  of  tungsten.  This  steel  is  used  for 
high-grade  saws  and  a  few  other  purposes.  Molybdenum  is 
more  expensive  than  tungsten. 

Cobalt  steel  has  practically  the  same  properties  and  uses  as 
tungsten  steel,  and  is  coming  into  use  in  the  making  of  high-speed 
tool  steels. 

341.  Copper  Steel. — Copper  steel  contains  from   1.0  to  4.0 
per  cent  of  copper.     Copper  steel  has  about  the  same  strength 
as  nickel  steel,  but  is  a  little  more  brittle  and  less  ductile.     Cop- 
per hardens  and  increases  the  strength  of  carbon  steels  without 
reducing  their  ductility.     If  the  copper  exceeds  4.0  per  cent,  the 
steel  is  very  difficult  to  roll.     Copper  increases  the  electrical 
resistance.     Copper  steel  costs  less  than  nickel  steel  and  has 
about  the  same  uses. 

342.  Some    Four   and   Five   Part   Alloys. — Chromium-nickel 
steel  has  great  strength  and  hardness.     Annealing  rolled  chro- 
mium-nickel steel  reduces  the  elastic  limit  and  ultimate  and 
increases  the  ductility,  while  hardening  the  steel  greatly  increases 
the  elastic  limit  and  ultimate  and  decreases  the  ductility.     The 
elastic  limit  may  vary  from  50,000  to  150,000  Ib.  per  square  inch, 
the  ultimate  strength  from  85,000  to  200,000  ,b.   per  square 
inch,  and  the  elongation  in  2  in.  from  35  to  2  per  cent,  depending 
upon  the  elements  present  and  the  heat  treatment.     Chromium- 
nickel  steels  are  used  in  making  automobiles,  guns,  armor,  safes, 
machine   parts,   gears,   axles,   etc.     In   making   armor   plate,   a 
plate  of  this  steel  is  heated  and  then  the  surface  is  suddenly 
cooled  with  a  cold  brine  spray,  thus  making  the  surface  very 
hard  and  strong  and  leaving  the  interior  more  tough. 

Chromium-vanadium  steel  has  a  very  high  strength  when 
tempered  properly.  Heat  treatments  have  about  the  same 
effect  on  this  steel  as  on  carbon  steels,  though  the  effect  is 
more  pronounced.  The  elastic  limit  may  vary  from  60,000 
to  190,000  Ib.  per  square  inch  and  the  ultimate  strength 


SPECIAL  STEELS  AND  CORROSION  OF  IRON  AND  STEEL    249 

from  90,000  to  210,000  Ib.  per  square  inch,  depending  on  the 
amounts  of  the  elements  present  and  the  heat  treatments. 
Chromium-vanadium  steel  is  used  for  locomotive  forgings,  shafts, 
springs,  tires,  tubes,  plates,  wire,  etc. 

Nickel-vanadium  steel  contains  about  0.20  per  cent  of  carbon, 
from  2  to  12  per  cent  of  nickel,  and  from  0.7  to  1.0  per  cent  of 
vanadium.  More  than  1.0  per  cent  of  vanadium  decreases 'the 
strength  and  increases  the  brittleness.  The  addition  of  vanadium 
to  a  nickel  steel  raises  the  ultimate  tensile  strength,  elastic 
limit,  toughness,  and  hardness  with  very  little  decrease  in 
ductility.  Tempering  improves  the  qualities.  The  strength 
of  this  steel  is  about  the  same  as  that  of  chromium-vanadium 
steel. 

Tungsten-chromium-vanadium  steel  usually  contains  from 
15  to  20  per  cent  of  tungsten,  3  to  5  per  cent  of  chromium, 
0.5  to  2.0  per  cent  of  vanadium,  0.60  to  0.80  per  cent  of  carbon, 
and  very  low  percentages  of  silicon,  sulphur,  and  phosphorus. 
When  properly  heat  treated,  this  steel  offers  a  very  high  resistance 
to  wear  at  ordinary  and  fairly  high  temperatures  (up  to  and 
including  a  red  heat)  besides  having  high  strength  and  fair 
ductility.  On  account  of  these  properties  this  steel,  which  is 
frequently  called  high-speed  steel,  is  used  for  cutting  tools  on 
metal  working  machinery  and  in  places  where  heat  and  wear  are 
to  be  resisted. 

C.  CORROSION  OF  IRON  AND  STEEL 

343.  Definition  of  Corrosion. — Corrosion  of  iron  and  steel  is  the 
oxidation  of  the  iron  due  to  the  formation  of  rust  or  the  gradual 
changing  of  the  iron  to  iron  oxide.  This  rust  will  form  rapidly 
upon  the  exposed  surfaces  of  the  iron  or  steel,  so  that  the  life  of  an 
unprotected  steel  structure  is  much  less  than  that  of  one  of 
stone  or  wood.  Rust  will  not  form  in  perfectly  dry  air.  An 
analysis  of  rust  taken  from  a  bridge  in  Conway,  Wales,  gave 
93.1  per  cent  of  Fe2O3,  5.8  per  cent  of  FeO,  and  0.9  per  cent  of 
carbon  dioxide. 

Any  unprotected  surface  of  iron  or  steel,  when  exposed  to  the 
atmosphere,  soon  becomes  covered  with  a  thin  layer  of  iron 
oxide,  which  tends  to  protect  the  surface  from  further  rusting. 
This  thin  layer  of  rust  does  practically  no  injury  to  the  metal. 
With  prolonged  exposure  to  moist  air,  this  film  of  oxide 


250 


MATERIALS  OF  CONSTRUCTION 


becomes  deeper  and  assumes  a  reddish-brown  color.  The  deeper 
the  film  of  rust,  the  more  the  metal  is  injured.  Sometimes 
the  corrosive  action  forms  pits  in  the  metal,  which  later  tend  to 
enlarge  and  become  deep  holes.  This  pitting  action  is  very 
injurious  and  also  difficult  to  stop  after  it  has  once  started. 

344.  The  Life  of  Iron  and  Steel  under  Corrosion. — Corrosion 
is  promoted  by  moisture,  carbon  dioxide,  smoke,  sulphurous 
vapors,  acid  vapors,  acid  waters,  salt  waters,  sewage,  decaying 
vegetable  or  animal  matter,  and  in  general  by  all  kinds  of 
impurities,  both  in  and  adjacent  to  the  steel.  Electrolytic 
action  and  electrolysis  also  originate  and  hasten  corrosion. 

It  is  thought  that  structural  steel  rusts  more  rapidly  than 
wrought  or  cast  iron,  but  this  has  not  been  definitely  proved. 
Overhead  bracing  of  bridges  exposed  to  the  smoke  of  passing 
locomotives  rusts  rapidly.  Old  wrought-iron  bridges  often  show 
less  corrosion  than  do  the  modern  steel  ones.  Metal  that  is 
subject  to  shocks  and  overstrain  is  more  liable  to  corrosion  than 
metal  subject  to  steady  stresses.  Because  they  are  more  homoge- 
neous, smooth  surfaces  rust  less  than  rough  surfaces.  Poor 
steel  containing  blowholes  and  imperfections  rusts  rapidly  for  the 
same  reason.  Steel  containing  few  impurities  rusts  less  than 
steel  containing  many  impurities. 

The  life  of  steel,  wrought  iron,  and  cast  iron  under  corrosion 
depends  on  the  amount  of  protection  that  has  been  given  to  the 
exposed  surfaces,  and  also  upon  the  condition  of  the  air  and 
water  surrounding  the  metal.  The  following  table  gives  an 
idea  of  the  life  of  unprotected  plates  under  certain  conditions: 

YEARS  OF  LIFE  OF  AN  UNPROTECTED  PLATE  OF  A  CERTAIN  SIZE 


Sea  A 

vater 

Fresh 

water 

Aii 

iviateriai 

Foul 

Clear 

Foul 

Clear 

Impure 

Pure 

Cast  iron  

15 

16 

26 

88 

21 

88 

Wrought  iron 

5 

8 

7 

81 

8 

81 

Steel 

5 

10 

9 

80 

8 

80 

Cast  iron,  skin  removed  .... 

4 

11 

14 

90 

12 

90 

Cast  iron,  galvanized  

11 

28 

30 

208 

50 

208 

345.  Theories  of  Corrosion. — The   carbon-dioxide  theory  of 
corrosion  is  that  carbon  dioxide  combines  with  the  iron  to  form 


SPECIAL  STEELS  AND  CORROSION  OF  IRON  AND  STEEL    251 

iron  carbonate.  Then,  under  the  action  of  free  oxygen  in  the  air, 
this  iron  carbonate  separates  into  iron  oxide  and  carbon  dioxide, 
thus  furnishing  a  new  supply  of  carbon  dioxide  so  that  the  process 
can  be  continued.  This  theory  does  not  give  a  complete  expla- 
nation of  corrosion  as  iron  will  often  rust  when  there  is  no  carbon 
dioxide  present. 

The  moisture  theory  of  corrosion  is  that  water  acts  upon  and 
combines  with  the  iron  producing  iron  oxide  and  hydrogen 
peroxide,  but  there  are  few  proofs  of  this  action.  It  is  true, 
however,  that  water  is  an  agency  that  promotes  corrosion, 
especially  when  it  contains  acids  or  sulphurous  compounds. 

The  electrolytic  theory  of  corrosion  is  that  the  corrosion  is 
caused  by  small  momentary  electric  currents  that  originate  at 
points  in  the  metal  where  it  is  not  homogeneous.  Impurities, 
large  grains,  roughness  of  surface,  non-uniformity  of  structure, 
etc.  appear  to  cause  a  difference  in  potential  in  neighboring  parts 
of  the  metal.  This  difference  of  potential  causes  small  currents 
to  flow,  and  these  currents  cause  the  oxidation  of  the  iron. 
The  electrolytic  theory  is  generally  accepted  as  the  best  theory 
yet  proposed,  even  though  the  proof  is  not  quite  complete. 

346.  Prevention  of  Corrosion  in  General. — In  general,  corro- 
sion may  be  prevented  by  excluding  the  water  and  the  atmosphere 
from  the  surfaces  of  the  metals  by  covering  them  with  preserva- 
tive coatings  of  oils,  paints,  varnishes,  tar  or  bituminous  com- 
pounds, concrete;  or  coating  or  plating  the  surfaces  with  alumi- 
num, tin,  nickel,  lead,  or  zinc,  or  sometimes  by  the  black  oxide  of 
iron.     For  surfaces  properly  protected,  the  figures  in  the  above 
table  for  the  life  of  metals  may  be  doubled  or  tripled  if  the 
metal  is  not  subject  to  shock  or  wear. 

The  resistance  of  steel  to  corrosion  may  be  increased  by  taking 
certain  precautions  in  the  manufacture  so  as  (1)  to  produce  a 
metal  containing  very  few  or  no  impurities  which  will  set  up  an 
electrolytic  action  with  the  iron ;  (2)  to  add  some  substance  to  the 
metal  which  will  act  to  inhibit  electrolysis  of  the  iron;  or  (3)  to 
roll  the  metal  in  special  rolls  so  as  to  make  a  special  fine  grained 
surface  that  is  very  dense  and  mechanically  resistant  to 
corrosion. 

347.  Prevention  of  Corrosion  by  Painting. — Painting  is  the 
usual  way  of  preserving  iron  and  steel  from  corrosion.     Some  of 
the  paints  used  are  asphalt,  chrome,  white  and  red  lead,  white 
zinc,  graphite,  and  iron  oxide  paints,  as  well  as  various  other 


252  MATERIALS  OF  CONSTRUCTION 

paints  and  varnishes  some  of  which  are  supposed  to  contain  rust 
repelling  or  resisting  constituents. 

The  surfaces  of  the  metal  must  be  thoroughly  cleaned.  Mud, 
dirt,  rust,  scale,  etc.  can  be  removed  with  steel  brushes, 
scrapers,  or  chisel  and  hammer.  The  use  of  a  sand  blast  is  the 
best  method  of  cleaning  metal  surfaces  before  painting.  Some- 
times rust  and  scale  are  removed  by  pickling  with  a  10  per  cent 
sulphuric  acid  solution.  All  traces  of  the  acid  must  be  removed 
by  washing,  and  the  metal  thoroughly  dried  before  painting. 

At  least  two  coats  of  paint  should  be  applied,  and  three  or 
four  coats  are  better.  Each  coat  of  paint  should  be  allowed  to 
dry  before  the  next  is  applied,  the  time  between  coats  being  at 
least  a  week.  The  paint  should  be  applied  in  a  smooth  even  coat 
(with  special  care  being  taken  at  the  angles  and  edges)  so  as  to 
form  an  impervious  film. 

One  gallon  of  paint  will  usually  cover  from  250  to  400  sq.  ft. 
as  a  first  coat,  depending  on  the  surface  conditions,  and  from 
350  to  500  sq.  ft.  as  a  second  coat. 

348.  Prevention  of  Corrosion  by  Covering  with  Concrete  or 
Asphalt. — Cement  mortar  or  concrete  will  protect  the  surfaces 
of  iron  and  steel  from  corrosion  when  the  metal  is  embedded  in 
the  mortar  or  concrete,  and  there  are  no  cracks  or  flaws  allowing 
the  penetration  of  water  or  other  corrosive  agents.     Oil  or  oil 
paints  should  not  be  used  on  iron  and  steel  that  are  to  be  placed  in 
concrete. 

Asphalt  will  protect  iron  and  steel  from  corrosion  if  it  is  applied 
in  appreciable  thickness  and  as  a  continuous  coat.  The  asphalt 
should  be  slightly  elastic,  when  cold,  should  have  a  high  melting 
point,  should  not  soften  much  at  100  degrees  Fahrenheit,  and 
should  be  applied  at  a  temperature  of  300  or  400  degrees  Fahren- 
heit. The  surface  of  the  metal  must  be  dry  and  should  be  hot, 
and  the  coating  should  be  of  considerable  thickness.  The  usual 
ways  of  applying  asphalt  are  either  by  dipping  the  metal  in  the 
asphalt  or  by  pouring  the  asphalt  on  the  metal. 

349.  Prevention  of  Corrosion  by  Galvanizing. — Galvanizing 
is  the  depositing  of  a  thin  coating  of  zinc  on  the  surfaces  of  iron 
or  steel.     Zinc  is  probably  the  best  preservative  of  iron  and  steel 
against  corrosion.     Besides  forming  a  complete  covering  for  the 
iron,  zinc  is  highly  electro-positive  with  respect  to  the  iron,  and 
the  iron  will  not  corrode  when  the  surfaces  of  the  two  metals  are 
in  contact.     When  two  metals  are  in  contact  with  each  other, 


SPECIAL  STEELS  AND  CORROSION  OF  IRON  AND  STEEL    253 

one  is  electro-positive  and  the  other  is  electro-negative.  The 
electro-positive  metal  may;  corrode  while  the  electro-negative 
metal  will  not  corrode. 

In  ordinary,  or  hot,  galvanizing,  the  articles  are  first  cleaned  by 
pickling  and  are  then  dipped  in  a  hydrochloric  acid  solution 
before  being  immersed  in  a  bath  of  molten  zinc  whose  temper- 
ature is  from  800  to  900  degrees  Fahrenheit.  When  the  articles 
have  reached  the  temperature  of  the  bath,  they  are  withdrawn, 
and  the  coating  is  set  in  water.  Wire,  bands,  and  similar  articles 
are  drawn  continuously  through  the  bath. 

Sheradizing  is  the  heating  of  the  iron  or  steel  articles  in  the 
presence  of  powdered  zinc,  which  forms  a  zinc  coating  on  them. 
A  closed  retort  is  used  and  the  temperature  is  below  the  melting 
point  of  the  zinc.  The  time  required  varies  from  30  minutes 
to  several  hours,  depending  on  conditions. 

The  American  standard  test  for  galvanized  wire  is  as  follows: 
Prepare  a  neutral  solution  of  sulphate  of  copper  (specific  gravity 
of  1.185).  Dip  the  wire  in  this  solution  for  1  minute,  wash, 
and  wipe  dry.  To  pass  the  test,  the  wire  must  stand  4  dips 
without  showing  a  permanent  coating  of  copper  on  any  part  of  the 
wire. 

350.  Prevention  of  Corrosion  by  Aluminum,  Nickel,  Tin,  or 
Lead  Plating. — Aluminum,  nickel,  tin,  or  lead  plating  consists 
of  depositing  a  thin  coating  of  one  of  these  metals  on  the  surfaces 
of  wrought  iron,  cast  iron,  or  steel  as  a  protection  from  corrosion. 
Good  aluminum  coatings  are  difficult  to  secure.     Nickel  plating 
makes  a  fine  appearing  surface  which  is  capable  of  taking  a  high 
polish.     Pinholes  are  often  found  in  tin  plating,  through  which 
the  atmosphere  can  attack  the  iron  and  cause  corrosion.     A  lead 
coating  is  a  good  protection  for  iron  and  steel,  provided  that  the 
coating  is  perfectly  gastight.     Sheets,  having  a  thin  coating  of 
lead,  are  known  as  terne  plates  and  are  not  very  durable. 

351.  Prevention  of  Corrosion  by  the  Inoxidation  Process.— 
This  process  is  the  forming  of  a  continuous  coating  of  black  oxide 
of  iron  over  the  surfaces  of  the  iron  or  steel.     This  coating  is 
stable  and  affords  good  protection  against  corrosion.     The  usual 
method  is  to  heat  the  articles  to  a  temperature  of  1,200  degrees 
Fahrenheit  or  more  in  a  closed  retort,  and  then  add  steam  (some- 
times partially  decomposed  steam)  at  a  temperature  of  1,200 
degrees  Fahrenheit  or  more  and  a  hydrocarbon  such  as  producer 
gas,  naphtha,  etc.     This  addition  of  steam  and  hydrocarbon 


254  MATERIALS  OF  CONSTRUCTION 

forms  a  film  of  iron  oxide  over  the  metal.  The  time  required 
varies  from  15  minutes  to  2  hours,  depending  on  the  details  of 
the  process  used  and  other  conditions. 


CHAPTER  XV 

NON-FERROUS  METALS  AND  THEIR  ALLOYS 
A.  THE  NON-FERROUS  METALS 

352.  General. — The  non-ferrous,   or  minor,   metals  may  be 
divided  into  three   classes  according  to  their  industrial  impor- 
tance.    In  the  first  class  are  aluminum,  copper,  lead,  nickel,  tin, 
and  zinc,  while  the  second  class  contains  antimony,  bismuth, 
cadmium,  gold,  silver,  mercury,  and  platinum.     The  third  class 
contains  metals  whose  chief  use  is  as  an  alloying  element,  such 
as  cobalt,    chromium,    magnesium,    manganese,   molybdenum, 
titanium,  tungsten,  vanadium,  etc. 

353.  Copper. — Copper  is  a  reddish  colored  metal  and,  next  to 
iron,  is  the  most  useful  and  valuable  metal.     It  occurs  in  native 
form  and  in  ores,  usually  as  a  sulphide  or  oxide.     The  most 
important  ore  is  copper  pyrites,  CuFeS2. 

The  methods  of  extracting  copper  from  its  ores  vary  greatly 
because  of  the  presence  of  different  impurities.  In  general,  the 
process  consists  of  (1)  roasting  to  remove  the  sulphur;  (2)  smelt- 
ing the  ore  in  a  blast  furnace  to  remove  most  of  the  gangue  as 
slag;  and  (3)  the  conversion  of  the  blast  furnace  product,  a 
mixture  of  metallic  sulphides,  called  "  matte,"  into  copper  by 
using  a  small  type  of  bessemer  converter.  After  this  the  copper 
is  refined,  usually  by  an  electrolytic  process,  to  make  it  purer. 

Native  copper  is  crushed,  concentrated,  smelted  in  a 
reverberatory  furnace,  and  then  refined. 

Copper  is  malleable  and  ductile  and  may  be  cast,  rolled  or 
drawn,  and  annealed.  It  oxidizes  at  a  red  heat  and  melts  at 
about  1,900  degrees  Fahrenheit.  Its  specific  gravity  varies 
from  about  8.6  in  castings  to  about  8.9  in  rolled  pieces.  Copper 
is  non-corrodible  in  dry  air.  One  of  the  most  important  proper- 
ties of  copper  is  its  high  electrical  conductivity,  which  increases 
with  its  purity.  The  modulus  of  elasticity  in  tension  is  about 
16,000,000  Ib.  per  square  inch.  The  following  table  gives 
average  values  of  the  tensile  strength: 

255 


256 


MATERIALS  OF  CONSTRUCTION 
TENSILE  STRENGTH  OF  COPPER 


Kind 

Elastic  limit, 
pounds  per 
square  inch 

Ultimate, 
pounds  per 
square  inch 

Per  cent 
elongation 

Cast 

8  000 

25  000 

Rolled 

15  000 

40  000 

Soft  wire  

15,000 

40  ,  000 

30 

Medium  wire  
Hard  wire  

25  ,  000 
35,000 

50  ,  000 
60  ,  000 

4 

2^ 

More  than  half  of  the  copper,  including  copper  wire,  is  used 
in  electrical  work;  about  one-fourth  in  brass  works;  and  the 
remainder  in  copper  sheets,  castings,  alloys,  etc. 

354.  Lead. — Lead  is  next  to  copper  in  commercial  importance. 
It  occurs  usually  as  a  sulphide  mixed  with  some  silver  or  anti- 
mony.    The  principal  ore  is  galena,   PbS.     Lead  is  extracted 
from  its  ores  by  first  roasting  the  ore  and  then  smelting  it  in  a 
blast  furnace.     Sometimes  the  silver   or  other  important  ele- 
ments are  removed.     If  the  lead  contains  too  many  impurities,  it 
is  refined. 

Lead  is  a  very  soft,  non-corrodible  (after  the  formation  of  an 
oxide  film  on  the  surface),  plastic,  inelastic,  bluish  white  metal 
with  a  very  low  strength.  Its  specific  gravity  is  about  11.3, 
and  its  melting  point  about  625  degrees  Fahrenheit.  The 
tensile  strength  of  lead  varies  from  1,600  to  2,400  Ib.  per  square 
inch.  Lead  flows  under  very  small  unit  loads;  is  malleable 
and  ductile;  and  can  be  drawn  into  wire. 

Lead  is  used  in  alloys,  plumbing  work,  paints,  chemical 
manufacture,  and  for  lead  pipes,  bullets,  linings  of  tanks,  chests, 
and  pipes,  etc. 

355.  Zinc. — Zinc  is  next  to  lead  in  order  of  importance.     It 
occurs  in  the  form  of  ores,  the  most  important  of  which  are  zinc 
blende,  ZnS,  calamine  or  zinc  spar,  ZnC03,  and  hemimorphite  or 
zinc  silicate,  Zn2SiO4.     Zinc   ores  are  usually  crushed,  concen- 
trated, calcined,  and  roasted,  after  which  the  zinc  is  distilled  and 
condensed.     This  crude  zinc,  or  "  spelter,"  must  be  refined  before 
using  if  there  is  too  much  lead  or  iron  present. 

Zinc  is  a  hard,  brittle,  bluish  white  metal  with  a  specific  gravity 
of  about  6.9  when  cast  and  7.1  when  rolled.  Its  fracture  is 


NON-FERROUS  METALS  AND  THEIR  ALLOYS  257 

crystalline  in  appearance.  The  principal  impurities  present  are 
lead,  iron,  and  cadmium.  -The  maximum  total  amount  of  these 
impurities  should  not  exceed  0.10  per  cent  for  high-grade  spelter, 
0.50  per  cent  for  intermediate  spelter,  1.20  per  cent  for  brass 
special,  with  no  limits  for  prime  western  and  dross  grades.  Lead 
makes  the  spelter  softer,  but  more  than  0.7  per  cent  causes 
cracking.  Iron  and  cadmium  make  the  spelter  harder  and  more 
brittle.  Cadmium  also  tends  to  increase  the  cracking.  Average 
values  for  strength  are:  5,000  Ib.  per  square  inch  for  tension, 
12,000  Ib.  per  square  inch  for  cross  bending,  and  20,000  Ib.  per 
square  inch  for  10  per  cent  compression. 

Zinc  is  used  for  galvanizing  and  alloys  principally,  and  also 
for  zinc  dust,  zinc  castings,  sheet  zinc,  etc. 

356.  Tin. — Tin  is  a  lustrous  white  metal  occurring  in  nature 
in  ores  which  may  be  found  in  lodes  or  veins  or  in  alluvial  deposits. 
The  principal  ore  is  cassiterite,  SnO2.     Tin  ore  is  first  concen- 
trated and  then  smelted,  after  which  the  crude  tin  is  refined. 

Tin  is  a  malleable  metal  with  a  specific  gravity  of  7.3  and  a 
melting  point  of  450  degrees  Fahrenheit.  Its  strength  is  about 
3,500  Ib.  per  square  inch  in  tension,  6,500  Ib.  per  square 
inch  in  compression,  and  4,000  Ib.  per  square  inch  in  cross 
bending. 

Tin  is  used  for  tin  plates,  tin  cans,  safety  plugs  for  boilers, 
household  articles,  tin  plating,  tin  foil,  etc. 

357.  Aluminum. — Aluminum  is  a  soft,  white,  malleable  metal 
that  is  found  in  nature  in  many  combinations.     The  two  most 
important  combinations  are  bauxite  (a  mixture  of  aluminum  and 
iron  hydrates  with  impurities)  and  cryolite  (a  mixture  of  sodium 
and  aluminum  fluoride).     The  principal  method  of  extraction  of 
aluminum     from    its    ores     consists    in    the     electrolysis     of 
comparatively  pure  aluminum  dissolved  in  a  bath  of  molten 
cryolite. 

The  melting  point  of  aluminum  is  1,150  degrees  Fahrenheit; 
the  specific  gravity  is  about  2.55  when  cast  and  2.75  when  rolled. 
Aluminum  may  be  obtained  from  99  to  99.5  per  cent  pure,  the 
most  common  impurities  being  iron  and  silicon.  Aluminum  is 
practically  free  from  corrosion,  can  be  annealed,  is  quite  ductile, 
and  shrinks  greatly  when  cast.  The  electrical  conductivity  of 
aluminum  is  from  ^  to  %  that  of  copper.  The  following  table 
gives  an  idea  of  the  average  strength  of  aluminum: 

17 


258 


MATERIALS  OF  CONSTRUCTION 
AVERAGE  STRENGTH  OF  ALUMINUM 


Tension 

Compression 

Tension  and 

Kind 

Elastic 
limit, 
pounds  per 
square  inch 

Ultimate, 
pounds  per 
square  inch 

Per  cent 
reduc- 
tion of 
area 

Elastic 
limit, 
pounds  per 
square  inch 

Ultimate, 
pounds  per 
square  inch 

modulus  of 
elasticity, 
pounds  per 
square  inch 

Cast  

8,000 

20  ,  000 

15 

4,000 

12,500 

9,000.000 

Rolled  

18,000 

30,000 

30 

4,000 

1  1  ,  500 

13,500,000 

Wire  drawn.  . 

25  ,  000 

45,000 

50 

17,000,000 

Aluminum  is  used  for  electrical  work,  alloys,  thermit  welding, 
wire,  cooking  utensils  and  where  a  strong,  light,  malleable,  and 
non-corrodible  cast  or  rolled  metal  is  desired. 

358.  Nickel. — Nickel  is  the  least  important  of  the  metals  of 
the  first  class  and  perhaps  it  should  be  included  in  the  third  class 
rather   than   the    first.     Its    principal   ores   are    nickel   pyrites 
(nickel   sulphide)    and   garnierite    (nickel   magnesium   silicate). 
The  sulphur  ore  is  first  roasted  and  then  smelted  in  a  blast 
furnace,  after  which  it  may  be  run  through  a  converter  to  remove 
the  iron  or  refined  to  remove  the  copper.     The  silica  ores  are 
first  mixed  with  some  sulphur  compounds,  smelted  in  a  blast  fur- 
nace, and  then  treated  in  the  same  ways  as  the  sulphur  ores. 

It  is  a  hard,  tough,  ductile,  malleable,  and  non-corrodible  metal 
of  a  silvery  white  color  and  is  capable  of  taking  a  high  polish. 
It  has  a  specific  gravity  varying  from  8.3  to  9.2,  and  a  melting 
point  of  3,000  degrees  Fahrenheit. 

Nickel  is  used  very  much  in  metal  plating  and  in  alloys  with 
copper  and  steel. 

359.  Gold,  Silver,  and  Platinum. — Gold  is  the  most  malleable 
and  ductile  of  all  metals.     One  ounce  Troy  can  be  beaten  to  cover 
160    sq.    ft.    of    surface    and    1    grain    can    be    drawn    into    a 
wire  500  ft.  long.     The  specific  gravity  of  pure  pressed  gold 
is  about  19.3.     The  melting  point  is  about  1,915  degrees  Fahren- 
heit.    Gold  is  used  for  coins,  ornaments,  plating,  etc. 

Silver  is  the  whitest  of  all  metals,  is  very  malleable  and  ductile, 
and  is  between  gold  and  copper  in  hardness.  The  specific  gravity 
varies  from  10  to  11.  The  melting  point  is  about  1,750  degrees 
Fahrenheit.  It  is  the  best  heat  conductor  of  all  metals,  and  is 
equal  to  copper  as  a  conductor  of  electricity.  Silver  is  used  for 
coins,  ornaments,  plating,  electrical  work,  etc. 

Platinum  is  a  malleable  and  very  ductile  metal  of  a  whitish  gray 


NON-FERROUS  METALS  AND  THEIR  ALLOYS  259 

color.  It  is  very  difficult  to  fuse.  Platinum  is  used  for  chemi- 
cal laboratory  vessels,  in  the  manufacture  of  electric  incandescent 
lamps  and  electric  contact  points,  for  standard  weights  and 
measures,  for  jewelry,  etc. 

360.  Some     Other    Non-ferrous    Metals. — Antimony    is    a 
brittle  metal  of  a  bluish-white  color  and  a  highly  crystalline  or 
laminated  structure.     It  has  a  specific  gravity  of  about  6.75. 
It  melts  at  842  degrees  Fahrenheit,  and  burns  in  air  with  a  bluish- 
white  flame.     Antimony  is  used  in  the  manufacture  of  alloys 
such  as  type  metals  and  unit  friction  metals. 

Bismuth  is  a  very  brittle  metal  of  a  light-reddish  color  and  a 
highly  crystalline  structure.  Its  specific  gravity  is  about  9.8. 
It  melts  at  510  degrees  Fahrenheit  and  boils  at  2,300  degrees 
Fahrenheit.  The  conductivity  for  electricity  is  about  J^o  that 
of  silver.  Bismuth  is  very  diamagnetic.  Its  tensile  strength 
is  about  6,400  Ib.  per  square  inch.  Bismuth  is  used  in  alloys. 

Cadmium  is  a  lustrous  bluish-white  metal  with  a  fibrous  frac- 
ture. Its  specific  gravity  is  about  8.65.  It  melts  below  500 
degrees  Fahrenheit  and  volatilizes  at  about  680  degrees  Fahren- 
heit. Cadmium  is  used  in  the  manufacture  of  fusible  alloys, 
etc. 

Magnesium  is  a  light,  malleable,  and  ductile  metal  of  brilliant 
silver-white  color.  It  is  non-corrosive.  It  is  highly  com- 
bustible and  burns  with  a  very  brilliant  light.  The  specific 
gravity  is  about  1.70.  It  melts  at  1,200  degrees  Fahrenheit. 
Magnesium  is  used  for  signal  lights,  flash  lights,  and  as  an  alloy 
with  aluminum. 

Manganese  has  a  specific  gravity  of  about  7.5.  It  is  used  as 
an  alloying  material  with  iron,  especially  in  the  manufacture  of 
steel,  and  also  as  an  alloy  with  steel. 

B.  ALLOYS  OF  NON-FERROUS  METALS 

361.  General. — An  alloy  is  made  by  combining  two  or  more 
metals,  when  in  a  molten  condition,  and  this  alloy  may  be  either  a 
solid  solution  of  the  metals  or  their  chemical  compounds,  or  a 
mixture  of  such  solutions.     The  physical  properties  of  an  alloy 
cannot  be  predicted  from  the  properties  and  proportions  of  the 
metals  used. 

362.  Brasses. — Ordinary  brasses  are  alloys  of  copper  and  zinc, 
while  special  brasses  contain  some  other  element  or  elements  in 


260 


MATERIALS  OF  CONSTRUCTION 


addition.  The  most  valuable  brasses  contain  from  65  to  80  per 
cent  of  copper  and  from  35  to  20  per  cent  of  zinc.  A  little  tin, 
about  1  or  2  per  cent,  is  usually  added  if  the  brass  is  to  be  turned 
or  planed.  These  mixtures  give  a  strong  ductile  alloy  that  can 
be  cast,  drawn,  or  rolled.  Brass  has  a  specific  gravity  of  8.95, 
can  be  annealed,  and  is  harder  and  more  ductile  than  copper. 
The  tensile  strength  of  brass  is  about  25,000  Ib.  per  square  inch, 
and  this  can  be  increased  by  rolling  or  drawing. 

The  addition  of  lead  to  brass  softens  it  and  lowers  the  strength 
and  ductility.  More  than  3  per  cent  of  lead  should  not  be  used 
because  of  the  danger  of  segregation. 

Aluminum,  up  to  5  per  cent,  increases  the  hardness,  elastic 
limit,  and  ultimate  in  tension,  but  decreases  the  ductility. 
Aluminum  brass  is  used  for  machine  castings,  forgings,  plates, 
etc.,  and  is  a  strong  non-corrosive  brass. 

The  most  valuable  special  brass  is  the  so-called  "  manganese 
bronze."  The  manganese  is  used  for  deoxidation  purposes  in 
the  manufacture,  and  the  resultant  brass  contains  practically  no 
manganese.  The  chemical  composition  is  variable;  one  being 
given  as  about  59  per  cent  of  copper,  40^  per  cent  of  zinc,  less 
than  0.5  per  cent  of  aluminum,  and  less  than  0.15  per  cent  of 
lead;  while  another  is.  given  as  57  per  cent  of  copper,  40  per 
cent  of  zinc,  1  per  cent  of  tin,  1%  per  cent  of  iron,  and  a  little 
aluminum.  As  the  range  of  composition  is  large,  the  properties 
vary  accordingly.  A  soft  grade  of  manganese  bronze  may  have 
a  tensile  strength  of  60,000  Ib.  per  square  inch  and  an  elongation 
of  over  40  per  cent  in  2  in.,  while  a  hard  grade  may  have  a 
tensile  strength  of  90,000  Ib.  per  square  inch  and  an  elonga- 
tion of  20  per  cent  in  2  in.  This  metal  has  great  strength  and 
toughness  and  can  be  cast  in  intricate  forms  successfully  besides 
being  highly  resistant  to  corrosion, 


AVERAGE  STRENGTH  OF  CAST  AND  ROLLED  MANGANESE  BRONZE 


Kind 

Tension,  pounds  per 
square  inch 

Per  cent 
elongation 
in  2  in. 

Compression,  pounds 
per  square  inch 

Elastic  limit 

Ultimate 

Elastic  limit 

Ultimate 

Cast  

30,000 
45,000 

75  ,  000 
95  ,  000 

28 
22 

37  ,  000 
55  ,  000 

95  ,  000 
140,000 

Rolled  or  forged  

NON-FERROUS  METALS  AND  THEIR  ALLOYS 


261 


Sterro  metal  is  brass  containing  about  lj^  per  cent  of  iron. 
The  iron  increases  the  strength  and  working  qualities. 

Delta  metal  is  brass  containing  about  3  per  cent  of  iron. 
When  delta  metal  is  cast,  its  tensile  strength  is  about  45,000  Ib.  per 
square  inch  with  an  elongation  of  about  10  per  cent  in  2  in.  When 
it  is  rolled,  its  strength  and  ductility  are  about  the  same  as  those 
of  medium  carbon  steel.  This  alloy  has  a  high  resistance  to 
corrosion. 

Tobin  bronze  is  similar  to  delta  metal  except  that  its  iron 
content  is  less  and  that  small  amounts  of  tin  and  lead  have 
been  added.  This  alloy  may  be  cast  or  rolled,  and  it  has  a 
high  tensile  strength  and  a  very  high  resistance  to  corrosion. 


APPROXIMATE  STRENGTH  OF  COPPER  ZINC  ALLOYS 


Per  cent 

Tensile 

Ultimate  strength  in  pounds 

Copper, 

Zinc, 

elonga- 

elastic limit, 

per  square  inch 

per  cent 

per  cent 

tion  in 
5  in. 

pounds  per 
square  inch 

Tension 

Com- 
pression 

Cross- 
bending 

100 

0 

7.0 

14,000 

27,000 

41,000 

30,000 

80 

20 

28.0 

8,000 

28,000 

40,000 

23,000 

70 

30 

22.0 

8,500           32,000 

45,000 

27,000 

60 

40 

20.0 

17,000           40,000 

75,000 

40,000 

50 

50 

5.0 

19,000            30,000 

115,000 

35,000 

20 

80 

0.5 

8,000 

10.000 

50,000 

23,000 

0 

100 

0.5 

4,000              5,500 

22,000 

7,000 

363.  Bronzes. — Bronzes  are  alloys  of  copper  and  tin.  They 
are  harder,  denser,  and  more  fusible  than  copper.  Practically  all 
of  the  commercial  bronzes  contain  less  than  25  per  cent  of  tin. 

The  addition  of  lead  increases  the  plasticity  of  bronzes.  Lead 
bronzes  are  used  for  bearings. 

Phosphor-bronze  is  a  bronze  containing  less  than  1  per  cent  of 
phosphorus.  The  addition  of  the  phosphorus  permits  the 
molding  of  very  perfect  castings.  This  bronze  is  hard  and 
tough,  and  its  tensile  strength  varies  from  40,000  to  100,000  Ib. 
per  square  inch.  It  is  used  for  bearings,  valve  seats,  telephone 
wire,  etc. 


262 


MATERIALS  OF  CONSTRUCTION 


APPROXIMATE  STRENGTH  OF  COPPER  TIN  ALLOYS 


Per  cent 

Tensile 

Ultimate  strength  in  pounds 

Copper, 

Zinc, 

elonga- 

elastic limit, 

per  square  inch 

per  cent 

per  cent 

tion  in 
5  in. 

pounds  per 
square  inch 

Tension 

Com- 
pression 

Cross- 
bending 

100 

0 

7.0 

14,000 

27,000 

41,000 

30,000 

95 

5 

12.0 

16,000 

30,000          42,000 

33,000 

90 

10 

5.0 

19,000           30,000          47,000 

39  ,  000 

80 

20 

0.05 

21,000 

35,000          75,000 

55,000 

75 

25 

0.0 

22,000 

22,000 

110,000 

32  ,  000 

70 

30 

0.0 

5,500 

5,500 

140,000 

12,000 

65 

35 

0.0 

2,200 

2,200 

85,000 

5,000 

45 

55 

0.0 

3,000 

3,000 

35,000 

5,000 

10 

90 

6.5 

3,500 

6,500 

10,000 

5,500 

0 

100 

35.0 

3,500 

6,500 

4,000 

364.  Various  Aluminum  Alloys. — Aluminum  bronze  is  not  a 
bronze,  but  is  a  copper  aluminum  alloy  containing  from  88  to 
95  per  cent  of  copper  and  from  12  to  5  per  cent  of  aluminum. 
This  alloy  is  very  strong  and  ductile,  but  it  shrinks  very  much  in 
casting.  With  10  per  cent  of  aluminum,  rolled  specimens  have 
an  elastic  limit  of  60,000  Ib.  per  square  inch,  an  ultimate  tensile 
strength  of  about  100,000  Ib.  per  square  inch,  and  an  elongation 
of  10  per  cent.  With  from  5  to  7  per  cent  of  aluminum,  the  alloy 
has  about  the  same  properties  as  medium  steel  and,  in  addition, 
is  non-corrosive.  The  modulus  of  elasticity  in  tension  is  about 
18,000,000  Ib.  per  square  inch. 

Aluminum  zinc  alloys  contain  up  to  33  per  cent  of  zinc  and  are 
light,  hard,  strong,  and  easily  made. 

Aluminum  copper  alloys  contain  up  to  8  per  cent  of  copper. 
The  copper  raises  the  yield  point  and  ultimate  strength  but 
greatly  lowers  the  ductility. 

Aluminum  magnesium  alloys,  "magnalium,"  contain  about 
\Yz  per  cent  of  magnesium  and  are  lighter,  stronger,  and  harder 
than  aluminum.  The  specific  gravity  is  2.5.  These  alloys  can 
be  forged,  rolled,  drawn,  machined,  and  filed.  They  take  a  high 
polish  and  are  resistant  to  oxidation. 

Aluminum-copper-zinc  alloys  contain  from  9  to  27  per  cent  of 
zinc  and  from  3  to  5  per  cent  of  copper.  These  alloys  are  strong 
but  not  ductile. 

In  aluminum-copper-tin  alloys  additions  up  to  7.5  per  cent  of 
copper  and  7.5  per -cent  of  tin  strengthen  the  aluminum.  Alloys 


NON-FERROUS  METALS  AND  THEIR  ALLOYS  263 

containing  from  20  to  60  per  cent  of  any  one  of  these  three 
metals  are  very  weak.  An  alloy  of  7.5  per  cent  of  copper,  7.5 
per  cent  of  tin,  and  85  per  cent  of  aluminum  has  a  tensile  strength 
of  about  30,000  Ib.  per  square  inch,  an  elongation  of  4  per  cent, 
and  a  specific  gravity  of  about  3.02. 

385.  Various  Nickel  Alloys. — Invar  is  an  alloy  containing 
about  36  per  cent  of  nickel,  63  per  cent  of  iron,  0.3  per  cent  of 
carbon,  and  0.7  per  cent  of  manganese.  It  has  a  very  low 
coefficient  of  expansion  (about  J^g  of  that  of  steel)  and  is  used 
for  steel  tapes  and  other  measuring  instruments. 

German  silver  is  composed  of  copper,  nickel,  and  tin  or  zinc 
in  varying  proportions.  The  best  varieties  contain  from  18 
to  25  per  cent  of  nickel,  25  to  30  per  cent  of  tin,  and  45  to  57  per 
cent  of  copper.  Sometimes  tin  is  used  instead  of  zinc,  producing 
an  inferior  alloy.  German  silver  is  used  for  ornaments,  table 
wear,  etc. 

Monel  metal  contains  about  72  per  cent  of  nickel,  1.5  per  cent 
of  iron,  and  26.5  per  cent  of  copper.  It  is  ductile,  flexible,  easily 
soldered,  has  a  high  resistance  to  corrosion,  and  is  suitable  for 
roofing.  The  ultimate  tensile  strength  of  castings  is  about 
75,000  Ib.  per  square  inch,  and  of  good  rolled  sheets  about 
100,000  Ib.  per  square  inch. 

Constantin  contains  about  40  per  cent  of  nickel  and  60  per  cent 
of  copper.  Its  electrical  resistance  is  from  28  to  30  times  that  of 
copper.  This  alloy  is  used  for  electrical  resistance  wire  and  also 
for  thermo-couples. 

Tableware  alloy  consists  of  25  per  cent  of  nickel,  25  per  cent 
of  zinc,  and  50  per  cent  of  copper. 

366.  Bearing  Metal  Alloys. — A  good  bearing  metal  should 
have  the  following  five  characteristics: 

1.  A  bearing  metal  must  be  strong  enough  to  carry  the  load 
without  any  distortion.     Some  loads  are  as  great  as  400  Ib.  per 
square  inch. 

2.  A  good  bearing  metal  should  not  heat  rapidly.     In  general, 
the  harder  the  bearing  metal,  the  more  likely  it  is  to  heat. 

3.  A  good  bearing  metal  should  work  well  in  the  foundry  and 
not  produce  spongy  castings. 

4.  A  good  bearing  metal  should  show  but  little  friction.     While 
friction  in  bearings  depends  largely  upon  the  lubricant  used,  the 
metal  also  has  some  influence. 

5.  Other  things  being  equal,  the  best  bearing  metal  is  the  one 
which  wears  the  slowest. 


264 


MATERIALS  OF  CONSTRUCTION 


The  principal  constituents  of  bearing  metals  are  copper,  tin, 
lead,  zinc,  antimony,  and  iron. 

PROPORTIONS  OF  SOME  BEARING  METALS 


Percentages  of 


-LYiiiu  ur  name 

Copper 

Tin 

Lead 

Zinc 

Antimony 

Iron 

Gun  metal 

90  0 

8  0 

2  0 

Babbitt  metal  
Repair  babbitt  
Bearing  metal  for  heavy 
bearings 

3.0 

77  0 

89.0 

8  0 

80.0 
15  0 

3.0 
20.0 

Engine  brass  
Heavy  bearings  
Ordinary  bearings  
White  metal 

76.5 
10.0 

5  0 

11.75 

15.0 
85  0 

65.0 
73.0 

11.75 

25.0 
12.0 
10  0 

Car  brass  lining  
American   anti-friction 
metal 

85.0 

78  5 

1  0 

15.0 
19  75 

0  75 

Car-box  metal  
Anti-friction  metal  
Ajax   metal    (arsenic    or 
phosphorus    0.4   per 
cent)  

81.25 

11.0 

84.5 
88.0 

7.25 

14.3 
12.0 

0.7 

Alloy  "B"  . 

77  0 

8  0 

15  0 

"K"  bronze  
Standard  (phosphorus  0.8 
per  cent^  .     ... 

77.0 

79  7 

10.5 
10  0 

12.5 
9.5 

367.  Fusible  Alloys. — The  following  table  gives  the  proportions 
of  some  fusible  alloys  and  their  approximate  melting  tempera- 
tures. Some  of  the  temperatures  may  be  inaccurate.  Fusible 
alloys  are  used  for  fusible  plugs  in  boilers,  etc. 


FUSIBLE  ALLOYS 

PROPORTIONS 

1  lead,  1  tin,  1  bismuth,  1  cadmium 

2  lead,  1  tin,  4  bismuth,  1  cadmium 

1  lead,  1  tin,  1  or  2  bismuth 

3  tin,  5  bismuth 

1  lead,  4  tin,  5  bismuth 

1  lead,  1  bismuth 

1  tin,  1  bismuth 

2  tin,  1  bismuth 

8  tin,  1  bismuth 

1  lead,  1  tin 

2  lead,  1  tin 


MELTING  TEMPERATURE 
IN  DEGREES  FAHRENHEIT 

155 

165 

200 

205 

240 

257 

285 

336 

392 

370  to  400 
440  to  475 


NON-FERROUS  METALS  AND  THEIR  ALLOYS 


265 


368.  Solders. — Common  solder  contains  about  1  part  tin  and 

1  part  lead;  fine  solder,  hard  solder,  and  plumbers'  solder  contain 

2  parts  tin  and  1  part  lead;  and  cheap  solder  contains  1  part  tin 
and  2  parts  lead. 

Common  pewter  contains  4  parts  lead  and  1  part  tin. 

Ordinary  gold  solder  contains  14  parts  gold,  6  parts  silver, 
and  1  part  copper. 

Silver  solder  contains  145  parts  silver,  73  parts  brass  (3  copper 
and  1  zinc),  and  4  parts  zinc. 

German  silver  solder  contains  38  parts  copper,  54  parts  zinc, 
and  8  parts  nickel. 

Aluminum  solder  contains  100  parts  tin  and  5  parts  lead  or 
zinc. 

369.  Composition  and  Use  of  Some  Miscellaneous  Alloys. — 


Name 

Copper 

Zinc 

Tin 

Lead 

Anti- 
mony 

Bis- 
muth 

Use 

Type  metal  

5 

75 

20 

Printing 

Hard  type  metal  

75 

25 

Printing 

Bell  metal 

75 

25 

'* 

Bells 

Best  valve  metal  

86 

2 

12 

Valves 

Valve  metal  

83 

15 

2 

Valves 

Tobin  bronze  

60 

38 

1H 

X 

Various  uses 

Naval  brass  

62 

37 

i 

On  ships 

Bush  metal  

80 

10 

5 

5 

Bushings 

Spring  brass  

66 

33 

1 

Springs 

Britannia  metal  

2 

82 

. 

16 

Ornaments,  etc. 

Pewter  

2 

89 

7 

2 

Plates,  toys,  etc. 

Muntz  metal  

60 

40 

Bolts,  valves,  etc. 

Admiralty  metal  

70 

29 

1 

Ship  condensers,  etc. 

370.  Corrosion  of  Non-ferrous  Metals  and  Their  Alloys.— 
The  non-ferrous  metals  and  their  alloys  offer  a  very  high  resist- 
ance to  corrosion.  They  may  be  said  to  be  non-corrodible  when 
compared  with  iron  and  steel.  Aluminum  and  nickel  are  two  of 
the  most  non-corrosive.  Lead  will  dissolve  in  water  to  a  slight 
extent,  but  this  is  stopped  when  the  carbonates  or  sulphates  of 
lime  deposited  on  the  lead  form  a  film  over  the  surface.  When 
zinc  is  exposed  to  the  atmosphere,  a  thin  skin  of  zinc  carbonate 
soon  forms  on  the  surface  and  prevents  further  corrosion.  Pure 
tin  offers  a  high  resistance  to  corrosion.  Copper  will  not  corrode 
when  exposed  to  dry  air,  but  it  will  corrode  slightly  when  there  is 
moisture  and  other  impurities  present  in  the  air. 

The  alloys  of  the  non-ferrous  metals  offer  practically  the  same 
resistance  to  corrosion  as  do  the  metals  themselves. 


CHAPTER  XVI 

SOME  MISCELLANEOUS  MATERIALS 

371.  Paints,  Oils,  and  Varnishes. — A  paint  is  composed  of  a 
base,  vehicle  or  binder,  and  a  solvent.  Most  paints  have  a  stain 
and  a  drier  added. 

The  base  of  a  paint  is  usually  white  lead  or  zinc  white,  though 
red  lead,  iron  oxide,  graphite,  etc.  are  sometimes  used.  White 
lead  is  a  combination  of  lead  carbonate  and  lead  hydrate.  The 
former  gives  the  body  and  the  latter  the  binding  properties  to 
the  paint.  White  lead  is  a  good  drier  of  linseed  oil,  and  very 
little  artificial  drier  is  needed.  Zinc  white  is  zinc  oxide.  It  is 
more  brilliant  but  less  permanent  than  white  lead.  Three  coats 
of  white  lead  are  equivalent  to  five  coats  of  zinc  white.  Red 
lead  is  a  double  oxide  of  lead.  It  makes  a  good  priming  paint 
for  new  wood  and  iron.  It  is  anti-corrosive,  resists  abrasion, 
and  is  a  good  drier  of  linseed  oil.  Iron  oxides  are  cheap  and 
serviceable  but  are  not  so  good  as  white  lead  and  zinc  white. 
Graphite  is  opaque  and  has  great  covering  power. 

The  usual  vehicle  or*  binder  is  linseed  oil.  Raw  linseed  oil  is 
obtained  from  flaxseed.  Boiled  linseed  oil  is  made  by  heating 
the  raw  oil  alone  or  with  a  little  drier.  Boiled  linseed  oil  dries 
in  half  the  time  required  for  raw  linseed  oil,  and,  consequently, 
the  boiled  oil  is  used  more  for  exterior  work  while  the  raw  oil  is 
used  for  interior  work.  Linseed  oil  is  often  adulterated  by  adding 
cottonseed,  resin,  hemp,  mineral,  or  fish  oils.  Fish  oil  and  cotton- 
seed oil  treated  with  benzine  are  sometimes  used  as  substitutes 
for  linseed  oil. 

Spirits  of  turpentine  is  the  best  solvent.  It  is  often  adulterated 
with  mineral  oils.  Benzine  and  naphtha  are  sometimes  used  as 
substitutes  for  turpentine. 

Staining  colors  or  pigments  are  used  for  coloring  paints  having 
a  white  base.  The  most  commonly  used  pigments  are  as  follows : 
for  black  color,  soot  and  charcoal  blacks;  red  color,  Venetian  red 
and  red  lead;  brown  color,  burned  umber  and  raw  and  burned 
sierras;  green  color,  chrome  green;  blue  color,  Prussian  blue  or 
ultramarine  blue.  By  using  different  amounts  and  mixtures  of 
the  pigments,  practically  any  color  and  shade  may  be  obtained. 

267 


268  MATERIALS  OF  CONSTRUCTION 

A  drier  is  a  lead  compound,  a  manganese  compound,  or  a 
mixture  of  these  two  which  is  soluble  in  oil.  These  compounds 
act  as  carriers  of  oxygen  and  thus  hasten  the  oxidation  and 
solidification  of  the  linseed  oil.  Only  a  very  small  amount  of 
drier  should  be  used  with  most  paints,  and  none  with  "  ready 
mixed"  and  varnish  paints. 

Asphalt  paints  are  made  by  dissolving  bitumen  in  paraffin, 
petroleum,  naphtha,  and  benzine.  These  paints  are  used  to 
protect  iron  and  steel  from  corrosion. 

Varnishes  are  made  by  dissolving  gums  or  resins  in  oil,  turpen- 
tine, or  alcohol.  Usually,  linseed  oil  is  used  with  fossil  resin,  and 
the  compound  thinned  with  turpentine.  When  the  varnish 
dries,  a  smooth,  solid,  and  transparent  resin  is  left  which  forms 
the  varnished  surfaces. 

The  purpose  of  a  paint  or  varnish  is  to  form  an  impervious 
coat  over  the  surface  of  the  material  to  which  it  is  applied  and  to 
keep  out  the  air  and  moisture  and  also  to  give  an  agreeable  color 
and  pleasing  appearance  to  the  material  painted. 

372.  Asbestos.— Asbestos  is  principally  a  silicate  of  magnesia 
with  more  or  less  water.     It  is  white  in  color  and  fibrous  in 
character.     The  fibers  are  hard  or  soft,  depending  on  the  amount 
of  water  present;  about  llj^  per  cent  or  less  of  water  causing  hard 
fibers  while  about  14  per  cent  of  water  makes  the  fibers  soft. 
Heating  asbestos  so  as  to  drive  out  the  water  makes  the  fibers 
very  brittle  and  crumbly. 

A  chemical  analysis  of  asbestos  will  give  results  approximately 
as  follows:  silica  40  to  41  per  cent;  magnesia  41  to  44  per  cent; 
ferrous  oxide  1  to  3  per  cent;  alumina  1  to  3  per  cent;  and  water 
llj^  to  14^  per  cent. 

The  thermal  conductivity  of  asbestos  is  about  0.0002. 

Asbestos  is  used  for  heat  insulation  purposes,  such  as  covering 
steam  pipes,  fire  curtains,  etc.  It  comes  in  the  form  of  fibers, 
boards,  cloth,  cylindrical  shapes,  etc.  The  fibers  may  be  mixed 
in  a  paste  and  applied  to  a  pipe  or  other  object. 

373.  Glass. — Ordinary  glass  is  made  by  fusing  together  sand 
or  silica  with  lime,  potash,  soda,  or  lead  oxide.     The  process  of 
manufacture  is  quite  complicated. 

Glass  is  a  hard,  brittle,  highly  elastic,  translucent,  and  com- 
monly transparent  substance  with  a  conchoidal  fracture.  Glass 
may  be  either  white  or  colored.  It  has  a  high  electrical 
resistance. 


SOME  MISCELLANEOUS  MATERIALS  269 

The  tensile  strength  of  ordinary  glass  varies  from  2,000  to 
3,000  Ib.  per  square  inch; -the  compressive  strength  from  6,000 
to  10,000  Ib.  per  square  inch;  the  cross-bending  strength  (modulus 
of  rupture)  from  3,000  to  4,000  Ib.  per  square  inch;  and  the 
modulus  of  elasticity  in  cross  bending  from  10,000,000  to  11,000,- 
000  Ib.  per  square  inch.  The  specific  gravity  of  glass  varies 
from  2.4  to  4.5,  but  is  usually  between  2.5  and  2.75,  giving  a 
weight  of  from  156  to  172  Ib.  per  cubic  foot. 

Glass  is  often  classified  according  to  its  thickness  into  "single 
strength,"  " double  strength,"  plate  glass,  etc.;  the  thickness 
usually  varying  from  ^Q  to  J^  in. 

Glass  is  used  for  windows,  skylights,  insulators,  mirrors, 
bottles,  dishes,  ornaments,  etc. 

Wire  glass  is  usually  ordinary  glass  containing  a  wire  mesh  in 
the  interior.  This  wire  mesh  is  usually  a  fine  woven  wire  which 
reinforces  the  glass  and  prevents  a  complete  failure  when  the 
glass  is  cracked  by  blows,  fire,  etc. 

374.  Glue. — Ordinary  glue  is  an  impure  gelatine  made  from 
bones,  skins,  or  fish  and  is  called  bone,  skin,  or  fish  glue  respec- 
tively.    A  good  quality  of  glue  should  be  free  from  all  specks  and 
grit,  have  a  uniform  light-brownish-yellow   color,   transparent 
appearance,  and  glassy  fracture.     Immersed  in  cold  water,  glue 
will  soften  and  swell  without  dissolving,   and  will  resume  its 
original  properties  upon  drying.     Glue  will  dissolve  in  hot  water 
and  form  a  thin  syrupy  liquid. 

The  adhesiveness  of  the  different  grades  of  glue  varies  con- 
siderably. The  hotter  the  glue,  the  better  the  joint.  Remelted 
glue  is  not  so  strong  as  that  freshly  prepared,  and  newly  manu- 
factured glue  is  not  so  good  as  old  glue.  The  ultimate  adhesive 
strength  of  wooden  surfaces  joined  with  glue  varies  from  1,200  to 
2,000  Ib.  per  square  inch  for  wood  joined  end  to  end  across  the 
grain,  and  from  350  to  1,000  Ib.  per  square  inch  for  wood  joined 
with  the  grain,  depending  upon  the  kind  of  wood,  the  quality  of 
the  glue,  and  the  workmanship. 

Glue  is  used  for  joining  the  surfaces  of  two  materials  together 
as  in  making  wooden  joints,  etc.  Special  kinds  of  glues  are 
manufactured  for  joining  different  materials  and  under  different 
conditions. 

375.  Rubber. — Almost  all  of  the  commercial  rubber  is  derived 
from  a  fluid  which  comes  from  the  outer  wood  of  several  species 
of  tropical  trees.     This  fluid   (called   " latex")   is  gathered  in 


270  MATERIALS  OF  CONSTRUCTION 

pails  and  then  coagulated  by  the  application  of  heat,  chemicals, 
or  mechanical  manipulation.  The  coagulated  mass  is  " cured" 
by  smoking,  and  is  then  known  as  " crude"  rubber.  The  crude 
rubber  is  washed,  shredded,  and  mixed  with  sulphur  and  other 
ingredients  and  then  rolled  into  sheets  (or  pressed  into  forms) 
after  which  it  is  " vulcanized"  by  heating  under  pressure. 

The  amount  of  sulphur  added  to  the  rubber  varies  from  about 
7  to  30  per  cent,  depending  on  the  hardness  desired.  Most  of 
the  rubber  used  in  engineering  contains  from  15  to  30  per  cent  of 
sulphur.  The  sulphur  also  makes  the  rubber  less  readily  softened 
by  heat  or  hardened  by  cold. 

The  specific  gravity  of  vulcanized  rubber  is  usually  taken  as  an 
index  of  its  value  or  quality  (though  often  untrue).  The  best 
grades  of  vulcanized  rubber  have  specific  gravities  that  are  less 
than  one. 

The  stress-strain  (load-deformation)  curve  for  a  good  grade  of 
rubber  in  tension  is  very  peculiar.  Up  to  about  30  per  cent  of 
the  ultimate  strength  there  is  an  increasing  rate  of  elongation 
with  increase  of  load,  then  the  rate  of  elongation  is  constant  for 
a  while,  and  later  the  rate  of  elongation  decreases  with  the 
increase  of  load.  Rubber  rarely  has  an  appreciable  permanent 
set,  even  though  stretched  nearly  to  the  ultimate  before  the 
load  is  released.  The  ultimate  tensile  strength  of  rubber  varies 
from  about  200  to  2,000  Ib.  per  square  inch,  depending  upon  the 
quality. 

Good  rubber  is  very  flexible  and  should  stretch  more  than  from 
five  to  eight  times  its  length  without  breaking,  depending  upon 
the  amount  of  metallic  oxides  contained  in  it.  The  permanent 
elongation,  measured  immediately  after  rupture,  of  good  rubber 
is  usually  less  than  12  per  cent  of  its  original  length. 

Whenever  rubber  is  subjected  to  a  cycle  of  stress,  where  the 
load  is  gradually  applied  and  then  gradually  released,  the  stress- 
strain  curve  exhibits  a  " mechanical  hysteresis"  or  loss  of  energy. 
All  of  the  mechanical  energy  applied  when  the  rubber  is  loaded 
is  not  returned  as  such  when  the  load  is  removed,  the  energy  not 
returned  being  dissipated  as  heat.  The  faster  the  rate  of  loading 
and  unloading,  the  greater  the  loss  of  mechanical  energy. 

Rubber,  unless  it  is  very  hard,  is  so  flexible  that  it  has  no  well 
defined  ultimate  strength  in  compression.  The  stress-strain 
curve  for  good  rubber  in  compression  is  slightly  concave  upwards. 
The  unit  stress  (when  the  specimen  is  compressed  to  about  half 


SOME  MISCELLANEOUS  MATERIALS  271 

its  original  height)  varies  from  about  400  to  1,000  Ib.  per  square 
inch,  depending  upon  the  quality  and  hardness  of  the 
rubber. 

Good  vulcanized  rubber  should  not  harden  appreciably  when 
exposed  to  cold. 

The  melting  point  of  rubber  is  about  375  degrees  Fahrenheit. 

Dilute  acids,  dilute  alkalis,  and  water  have  but  little  effect  on 
rubber. 

Oil  makes  the  rubber  brittle  and  shortens  its  "life." 

Vulcanized  rubber  tends  to  become  hard  and  brittle  with 
the  lapse  of  time  and  to  lose  its  "life"  or  ability  to  stretch.  The 
loss  of  "life"  or  the  ability  to  stretch  is  hastened  by  the  presence 
of  metallic  oxides  (such  as  chalk  or  zinc  oxide)  in  the  vulcanized 
rubber. 

Rubber  is  used  for  belting,  electrical  insulation,  floor  coverings, 
vehicle  tires  (solid  and  pneumatic),  toilet  articles,  rulers  and 
scales,  articles  of  clothing,  rubber  bands,  erasers,  hose,  and  many 
other  purposes. 

376.  Leather. — Leather  is  an  imputrescible  material  made 
from  the  hides  and  skins  of  living  creatures  by  chemical  and 
mechanical  treatment. 

Leather  may  be  classified  according  to  the  process  of  manu- 
facture as  follows: 

1.  Tanned  leather  in  which  the  hides  and  skins  are  combined 
with  tannin  or  tannic  acid. 

2.  Tanned  leather  in  which  the  skins  are  prepared  with  mineral 
salts. 

3.  Chamoised  leather  in  which  the  skins  are  rendered  imputres- 
cible by  treatment  with  oils  or  fats,  the  decomposition  products 
of  which  are  the  actual  tanning  agents. 

Leather  may  also  be  classified  according  to  the  kind  of  animal 
(ox,  heifer,  cow,  bull,  calf,  goat,  sheep,  horse,  etc.)  it  comes  from 
and  also  according  to  the  country  or  part  of  the  world  where  the 
animals  were  raised.  Ox  and  heifer  hides  are  the  best,  followed 
by  cow  and  bull  hides  respectively. 

The  properties  of  leather  are  affected  by  the  processes  of 
tanning,  finishing,  currying  (working  oil  or  grease  into  the 
leather),  etc.,  in  preparing  the  hides  for  use.  The  average 
tensile  strength  of  leather  is  from  2,000  to  3,000  Ib.  per  square 
inch.  The  weight  of  well-tanned  leather  is  about  62^  Ib.  per 
cubic  foot. 


272  MATERIALS  OF  CONSTRUCTION 

Leather  is  used  for  shoes,  belting,  gloves,  clothes,  book  binding, 
bags,  trunks,  etc. 

Rawhide  is  untanned  leather.  When  sound,  rawhide  is  about 
one  and  a  half  times  as  strong  as  tanned  leather  and  offers  a 
greater  resistance  to  impact  loads.  Rawhide  is  used  for  textile 
machinery  connections,  looms,  ships,  tiller  ropes,  etc. 

377.  Paper. — Paper  may  be    classified  according  to  use  into 
four  classes,  namely:  (1)  writing  and  drawing  papers,  (2)  print- 
ing and  newspapers,   (3)  wrapping  papers,  and  (4)  tissue   and 
cigarette  papers. 

The  process  of  paper  manufacture  consists  essentially  of  two 
main  divisions:  (1)  The  treatment  of  the  raw  material,  including 
cleaning,  dusting,  boiling,  washing,  bleaching,  and  reducing  to  a 
pulp;  (2)  the  methods  by  which  the  prepared  pulp  or  fibers  are 
converted  into  paper  ready  for  the  market,  and  these  include  the 
operations  of  beating,  sizing,  coloring,  surfacing,  cutting,  etc. 

The  materials  most  commonly  used  in  the  manufacture  of 
paper  are  rags,  straw,  and  wood. 

Most  of  the  paper  used  for  structural  purposes  comes  under 
the  third  class.  Ordinary  building  paper  is  a  wrapping  paper 
which  is  placed  in  the  walls  or  roofs  as  an  added  protection 
against  the  passage  of  air  and  heat.  Tarred  paper  is  paper 
covered  or  soaked  with  tar  which  tends  to  prevent  the  passage 
of  moisture.  Sometimes  an  ornamented  or  decorated  paper  is 
pasted  on  the  walls  and  ceilings  of  rooms  to  improve  their 
appearance. 

378.  Canvas. — Canvas  is  a  heavy,  strong,  coarse  cloth  made 
from  flax,  hemp,  tow,  jute,  or  cotton.     The  cloth  may  be  of  a 
natural  color,  bleached,  or  dyed.     Common  colors  are  white  and 
tan. 

Two  or  more  ply  yarns  are  used,  and  the  cloth  is  woven  loosely 
or  closely  as  desired.  The  quality  is  determined  by  the  yarn 
used,  the  closeness  of  weaving,  and  the  weight  and  strength  in 
tension.  The  tensile  strength  of  canvas  varies  from  3,000  to 
10,000  Ib.  per  square  inch. 

Canvas  is  used  for  bags,  tarpaulins,  sails,  belts,  tents,  etc. 

379.  Ropes. — Ropes  are  said  to  include  all  large  cords  more 
than  a  half  inch  in  diameter. 

Ordinary  rope  is  made  by  spinning  the  fibers  of  the  material 
together  to  make  a  yarn,  twisting  from  twenty  to  eighty  pieces 
of  yarn  together  to  form  a  strand,  and  then  twisting  three  or  four 


SOME  MISCELLANEOUS  MATERIALS  273 

strands  to  form  a  3  or  4  ply  rope.  In  each  case  of  twisting,  the 
direction  of  the  twist  is  reversed  so  that  the  rope  will  not  untwist 
when  loaded. 

Wire  rope  is  made  by  twisting  4,  7,  12,  19,  or  37  wires  together 
to  form  a  strand,  and  then  twisting  a  number  of  strands  together 
to  form  a  rope.  Frequently,  a  hemp  or  manila  rope  is  used  for  a 
core.  Hoisting  ropes  usually  have  19  wires  to  the  strand,  while 
7  or  12  wires  to  the  strand  are  used  for  standing  ropes,  rigging, 
etc. 

Great  care  must  be  taken  in  tying  or  splicing  ropes  together  so 
that  the  strength  will  not  be  reduced  too  much.  A  good  splice 
or  knot  should  have  about  80  per  cent  of  the  strength  of  the  rope. 

The  factor  of  safety  for  rope  varies  from  about  5  to  35,  depend- 
ing upon  the  kinds  of  loads,  the  speed  at  which  the  ropes  are 
worked,  the  diameter  of  the  pulley  blocks,  etc. 

The  following  table  gives  approximate  values  of  the  ultimate 
tensile  strength  of  several  kinds  of  rope.  The  unit  stresses  are 
based  on  the  original  gross  cross-sectional  area  of  the  rope. 

TENSILE  STRENGTH  OF  ROPE 

TENSILE  STRENGTH  IN  POUNDS 
KIND  OF  ROPE  PER  SQUARE  INCH 

Wire  (iron  and  steel) 50 , 000  to  90 , 000 

Cotton 5, 000 to    8,000 

Hemp 5,000to    8,000 

Manila ..  5, 000  to  10,000 

380.  Belts. — Rubber  belts  are  made  by  weaving  cotton  canvas 
of  the  required  length  and  width  and  then  covering  the  canvas 
with  vulcanized  rubber.  The  belts  may  be  of  2,  3,  or  4  ply 
(thicknesses  or  layers  of  canvas  and  rubber)  according  to  the 
power  to  be  transmitted.  Rubber  belts  are  stronger  than  leather 
belts,  usually  run  smoother  and  truer,  have  a  higher  coefficient 
of  friction,  and  are  impervious  to  water,  but  they  may  be  injured 
more  by  slipping  when  overloaded.  The  tensile  strength  of 
rubber  belting  varies  from  about  2,200  to  3,800  Ib.  per  square 
inch  on  the  average. 

Leather  belts  should  be  made  from  the  best  quality  of  well 
tanned  ox  hides.  The  hides  should  be  cut  in  strips  from  4  to 
6  ft.  long  and  about  Y\§  in.  thick,  and  then  scarfed,  spliced,  and 
cemented  end  to  end  to  make  the  desired  length  of  belt.  Accord- 
ing to  the  strength  required,  the  strips  of  leather  are  riveted  or 
cemented  together  in  thicknesses  to  form  " single"  or  " double " 

18 


274  MATERIALS  OF  CONSTRUCTION 

strength  belts.  For  light  loads,  the  " single"  strength  belt  gives 
the  greater  adhesion,  but  the  " double"  strength  belt  is  necessary 
for  heavy  loads.  The  " flesh"  side  of  the  belt  is  usually  placed 
next  to  the  pulley  as  it  gives  the  best  wear,  though  the  " grain" 
side  of  the  belt  gives  the  best  adhesion.  Tensile  tests  on  leather 
belts  have  given  results  varying  from  1,500  to  5,500  Ib.  per  square 
inch,  but  the  strength  of  the  average  belt  is  probably  nearer  the 
lower  value. 

Canvas  belts  are  sometimes  used,  but  they  give  much  poorer 
service  than  good  rubber  or  leather  belts  as  the  adhesion  and  life 
are  less.  The  strength  of  canvas  belts  in  tension  varies  from 
3,000  to  8,000  Ib.  per  square  inch. 

Great  care  must  be  taken  in  splicing  belts  so  as  to  secure  a  good 
joint.  Most  canvas,  rubber,  and  leather  belts  are  spliced  by 
lacing  or  riveting  and  rarely  by  sewing  or  gluing.  Splicing  a  belt 
reduces  its  strength  about  one-half;  consequently,  a  belt  should 
be  made  of  the  desired  length  so  as  to  require  no  shortening  or 
lengthening. 

Thin  flat  bands  of  tempered  steel  have  been  used  for  belts  in 
special  cases.  These  belts  are  very  strong,  have  but  little  slip, 
have  a  very  high  efficiency,  may  be  run  at  very  high  speeds,  and 
require  about  J^  of  the  width  of  a  good  leather  belt  for  the  same 
power. 


APPENDIX  A 
AMERICAN  SOCIETY  FOR  TESTING  MATERIALS 

PHILADELPHIA,  PA.,  U.  S.  A. 

AFFILIATED    WITH   THE 

INTERNATIONAL  ASSOCIATION  FOR  TESTING  MATERIALS 

STANDARD  SPECIFICATIONS  AND  TESTS 

FOR 
PORTLAND  CEMENT 

Serial  Designation :  C  9-21 

These  specifications  and  tests  are  issued  under  the  fixed  designation  C  9; 
the  final  number  indicates  the  year  of  original  adoption  as  standard,  or  in 
the  case  of  revision,  the  year  of  last  revision. 

ADOPTED,  1904;  REVISED,  1908,  1909,  1916,  1920  (EFFECTIVE  JAN.  1,  1921) 


These  specifications  were  approved  January  15,  1921, 

as  "Tentative  Standard'*  by  the 
American  Engineering  Standards  Committee 


SPECIFICATIONS 

1.  Definition. — Portland  cement  is  the  product  obtained  by  finely  pul- 
verizing clinker  produced  by  calcining  to  incipient  fusion  an  intimate  and 
properly  proportioned  mixture  of  argillaceous  and  calcareous  materials, 
with  no  additions  subsequent  to  calcination  excepting  water  and  calcined  or 
uncalcined  gypsum. 

T.  CHEMICAL  PROPERTIES 

2.  Chemical  Limits. — The  following  limits  shall  not  be  exceeded: 

Loss  on  ignition,  per  cent 4 . 00 

Insoluble  residue,  per  cent 0 . 85 

Sulfuric  anhydride   (SO3),  per  cent 2.00 

Magnesia  (MgO),  per  cent 5 . 00 

II.  PHYSICAL  PROPERTIES 

3.  Specific  Gravity. — The  specific  gravity  of  cement  shall  be  not  less  than 
3.10    (3.07   for   white    portland    cement).     Should  the  test  of  cement  as 
received  fall  below  this  requirement  a  second  test  may  be  made  upon  an  ig- 

275 


276    .  MATERIALS  OF  CONSTRUCTION 

nited  sample.     The  specific  gravity  test  will  not  be  made  unless  specifically 
ordered. 

4.  Fineness. — The  residue  on  a  standard  No.  200  sieve  shall  not  exceed 
22  per  cent  by  weight. 

5.  Soundness. — A  pat  of  neat  cement  shall  remain  firm  and  hard,  and 
show  no  signs  of  distortion,  cracking,  checking,  or  disintegration  in  the 
steam  test  for  soundness. 

6.  Time  of  Setting. — The  cement  shall  not  develop  initial  set  in  less  than 
45  minutes  when  the  Vicat  needle  is  used  or  60  minutes  when  the  Gillmore 
needle  is  used.     Final  set  shall  be  attained  within  10  hours. 

7.  Tensile  Strength. — The  average  tensile  strength  in  pounds  per  square 
inch  of  not  less  than  three  standard  mortar  briquettes   (see  Section  50) 
composed  of  1  part  cement  and  3  parts  standard  sand,  by  weight,  shall  be 
equal  to  or  higher  than  the  following: 


Age  at  test, 
days 

Storage  of  briquettes 

Tensile  strength, 
pounds  per 
square  inch 

7 

1  dav  in  moist  air,    6  days  in  water 

200 

28 

1  day  in  moist  air,  27  days  in  water  

300 

8.  The  average  tensile  strength  of  standard  mortar  at  28  days  shall  be 
higher  than  the  strength  at  7  days. 

III.  PACKAGES,  MARKING  AND  STORAGE 

9.  Packages  and  Marking. — The  cement  shall  be  delivered  in  suitable 
bags  or  barrels  with  the  brand  and  name  of  the  manufacturer  plainly  marked 
thereon,  unless  shipped  in  bulk.     A  bag  shall  contain  94  Ib.  net.     A  barrel 
shall  contain  376  Ib.  net. 

10.  Storage. — The  cement  shall  be  stored  in  such  a  manner  as  to  permit 
easy  access  for  proper  inspection  and  identification  of  each  shipment,  and 
in  a  suitable  weather-tight  building  which  will  protect  the  cement  from 
dampness. 

IV.  INSPECTION 

11.  Inspection. — Every  facility  shall  be  provided  the  purchaser  for  care- 
ful sampling  and  inspection  at  either  the  mill  or  at  the  site  of  the  work,  as 
may  be  specified  by  the  purchaser.     At  least  10  days  from  the  time  of 
sampling  shall  be  allowed  for  the  completion  of  the  7-day  test,  and  at  least 
31  days  shall  be  allowed  for  the  completion  of  the  28-day  test.     The  cement 
shall  be  tested   in   accordance  with  the  methods  hereinafter  prescribed. 
The  28-day  test  shall  be  waived  only  when  specifically  so  ordered. 

V.  REJECTION 

12.  Rejection. — The  cement  may  be  rejected  if  it  fails  to  meet  any  of  the 
requirements  of  these  specifications. 


APPENDIX  A  277 

13.  Cement  shall  not  be  rejected  on  account  of  failure  to  meet  the  fine- 
ness requirement  if  upon  retest  after  drying  at  100  degrees  Centigrade  for 
1  hour  it  meets  this  requirement. 

14.  Cement  failing  to  meet  the  test  for  soundness  in  steam  may  be  ac- 
cepted if  it  passes  a  retest  using  a  new  sample  at  any  time  within  28  days 
thereafter. 

15.  Packages  varying  more  than  5  per  cent  from  the  specified  weight  may 
be  rejected;  and  if  the  average  weight  of  packages  in  any  shipment,  as 
shown  by  weighing  50  packages  taken  at  random,  is  less  than  that  specified, 
the  entire  shipment  may  be  rejected. 


TESTS 
VI.  SAMPLING 

16.  Number  of  Samples. — Tests  may  be  made  on  individual  or  composite 
samples  as  may  be  ordered.     Each  test  sample  should  weigh  at  least  8  Ib. 

17.  (a)  Individual  Sample. — If  sampled  in  cars,  one  test  sample  shall  be 
taken  from  each  50  bbl.  or  fraction  thereof.     If  sampled  in  bins,  one  sample 
shall  be  taken  from  each  100  bbl. 

(6)  Composite  Sample. — If  sampled  in  cars,  one  sample  shall  be  taken 
from  one  sack  in  each  40  sacks  (or  1  bbl.  in  each  10  bbl.)  and  combined  to 
form  one  test  sample.  If  sampled  in  bins  or  warehouses,  one  test  sample 
shall  represent  not  more  than  200  bbl. 

18.  Method  of  Sampling. — Cement  may  be  sampled  at  the  mill  by  any 
of  the  following  methods  that  may  be  practicable,  as  ordered : 

(a)  From  the  Conveyor  Delivering  to  the  Bin. — At  least  8  Ib.  of  cement 
shall  be  taken  from  approximately  each  100  bbl.  passing  over  the  conveyor. 

(6)  From  Filled  Bins  by  Means  of  Proper  Sampling  Tubes. — Tubes  inserted 
vertically  may  be  used  for  sampling  cement  to  a  maximum  depth  of  10  ft. 
Tubes  inserted  horizontally  may  be  used  where  the  construction  of  the  bin 
permits.  Samples  shall  be  taken  from  points  well  distributed  over  the  face 
of  the  bin. 

(c)  From  Filled  Bins  at  Points  of  Discharge. — Sufficient  cement  shall  be 
drawn  from  the  discharge  openings  to  obtain  samples  representative  of  the 
cement  contained  in  the  bin,  as  determined  by  the  appearance  at  the  dis- 
charge openings  of  indicators  placed  on  the  surface  of  the  cement  directly 
above  these  openings  before  drawing  of  the  cement  is  started. 

19.  Treatment  of  Sample. — Samples   preferably  shall  be  shipped  and 
stored  in  air-tight  containers.     Samples  shall  be  passed  through  a  sieve 
having  20  meshes  per  linear  inch  in  order  to  thoroughly  mix  the  sample, 
break  up  lumps,  and  remove  foreign  materials. 

VII.  CHEMICAL  ANALYSIS 

Loss  on  Ignition   ' 

20.  Method. — One  gram  of  cement  shall  be  heated  in  a  weighed  covered 
platinum  crucible,  of  20  to  25  c.c.  capacity,  as  follows,  using  either  method 
(a)  or  (6)  as  ordered : 


278  MATERIALS  OF  CONSTRUCTION 

(a)  The  crucible  shall  be  placed  in  a  hole  in  an  asbestos  board,  clamped 
horizontally  so  that  about  three-fifths  of  the  crucible  projects  below,  and 
blasted  at  a  full  red  heat  for  15  minutes  with  an  inclined  flame;  the  loss  in 
weight  shall  be  checked  by  a  second  blasting  for  5  minutes.  Care  shall  be 
taken  to  wipe  off  particles  of  asbestos  that  may  adhere  to  the  crucible  when 
withdrawn  from  the  hole  in  the  board.  Greater  neatness  and  shortening 
of  the  time  of  heating  are  secured  by  making  a  hole  to  fit  the  crucible  in  a 
circular  disk  of  sheet  platinum  and  placing  this  disk  over  a  somewhat  larger 
hole  in  an  asbestos  board. 

(6)  The  crucible  shall  be  placed  in  a  muffle  at  any  temperature  between 
900  and  1,000  degrees  Centigrade  for  15  minutes  and  the  loss  in  weight 
shall  be  checked  by  a  second  heating  for  5  minutes. 

21.  Permissible    Variation. — A    permissible    variation    of   0.25   will    be 
allowed,  and  all  results  in  excess  of  the  specified  limit  but  within  this  per- 
missible variation  shall  be  reported  as  4  per  cent. 

Insoluble  Residue 

22.  Method. — To  a  1-gram  sample  of  cement  shall  be  added  10  c.c.  of 
water  and  5  c.c.  of  concentrated  hydrochloric  acid;  the  liquid  shall  be  warmed 
until  effervescence  ceases.     The  solution  shall  be  diluted  to  50  c.c.  and 
digested  on  a  steam  bath  or  hot  plate  until  it  is  evident  that  decomposition 
of  the  cement  is  complete.     The  residue  shall  be  filtered,  washed  with  cold 
water,  and  the  filter  paper  and  contents  digested  in  about  30  c.c.  of  a  5  per 
cent  solution  of  sodium  carbonate,  the  liquid  being  held  at  a  temperature 
just  short  of  boiling  for  15  minutes.     The  remaining  residue  shall  be  filtered, 
washed  with  cold  water,  then  with  a  few  drops  of  hot  hydrochloric  acid,  1 :9, 
and  finally  with  hot  water,  and  then  ignited  at  a  red  heat  and  weighed  as 
the  insoluble  residue. 

23.  Permissible    Variation. — A    permissible    variation    of    0.15    will   be 
allowed,  and  all  results  in  excess  of  the  specified  limit  but  within  this  per- 
missible variation  shall  be  reported  as  0.85  per  cent. 

Sulfuric  Anhydride 

24.  Method. — One  gram  of  the  cement  shall  be  dissolved  in  5  c.c.  of 
concentrated  hydrochloric  acid  diluted  with  5  c.c.  of  water,  with  gentle 
warming;  when  solution  is  complete,  40  c.c.  of  water  shall  be  added,  the 
solution  filtered,  and  the  residue  washed  thoroughly  with  water.     The  solu- 
tion shall  be  diluted  to  250  c.c.,  heated  to  boiling,  and  10  c.c.  of  a  hot  10- 
per-cent  solution  of  barium  chloride  shall  be  added  slowly,  drop  by  drop, 
from  a  pipette  and  the  boiling  continued  until  the  precipitate  is  well  formed. 
The  solution  shall  be'  digested  on  the  steam  bath  until  the  precipitate  has 
settled.     The  precipitate  shall  be  filtered,  washed,  and  the  paper  and  con- 
tents placed  in  a  weighed  platinum  crucible  and  the  paper  slowly  charred 
and  consumed  without  flaming.     The  barium  sulfate  shall  then  be  ignited 
and  weighed.     The  weight  obtained  multiplied  by  34.3  gives  the  percentage 
of  sulfuric  anhydride.     The  acid  filtrate  obtained  in  the  determination  of 
the  insoluble  residue  may  be  used  for  the  estimation  of  sulfuric  anhydride 
instead  of  using  a  separate  sample. 


APPENDIX  A  279 

25.  Permissible    Variation. — A   permissible   variation    of    0.10   will   be 
allowed,  and  all  results  in  excess  of  the  specified  limit  but  within  this  per- 
missible variation  shall  be  reported  as  2.00  per  cent. 

Magnesia 

26.  Method. — To  0.5  gram  of  the  cement  in  an  evaporating  dish  shall  be 
added  10  c.c.  of  water  to  prevent  lumping  and  then  10  c.c.  of  concentrated 
hydrochloric  acid.     The  liquid  shall  be  gently  heated  and  agitated  until 
attack  is  complete.     The  solution  shall  then  be  evaporated  to  complete 
dryness  on  a  steam  or  water  bath.     To  hasten  dehydration  the  residue  may 
be  heated  to  150  or  even  200  degrees  Centigrade  for  %  to  1  hour.     The 
residue  shall  be  treated  with   10  c.c.  of  concentrated  hydrochloric  acid 
diluted  with  an  equal  amount  of  water.     The  dish  shall  be  covered  and 
the  solution  digested  for  10  minutes  on  a  steam  bath  or  water  bath.     The 
diluted  solution  shall  be  filtered  and  the  separated  silica  washed  thoroughly 
with  water.1     Five  cubic  centimeters  of  concentrated  hydrochloric  acid 
and  sufficient  bromine  water  to  precipitate  any  manganese  which  may  be 
present  shall  be  added  to  the  filtrate  (about  250  c.c.).     This  shall  be  made 
alkaline  with  ammonium  hydroxide,  boiled  until  there  is  but  a  faint  odor 
of  ammonia,  and  the  precipitated  iron  and  aluminum  hydroxides,  after 
settling,  shall  be  washed  with  hot  water,  once  by  decantation  and  slightly 
on  the  filter.     Setting  aside  the  filtrate,  the  precipitate  shall  be  transferred 
by  a  jet  of  hot  water  to  the  precipitating  vessel  and  dissolved  in  10  c.c.  of 
hot  hydrochloric  acid.     The  paper  shall  be  extracted  with  acid,  the  solu- 
tion and  washings  being  added  to  the  main  solution.     The  aluminum  and 
iron  shall  then  be  reprecipitated  at  boiling  heat  by  ammonium  hydroxide 
and  bromine  water  in  a  volume  of  about  100  c.c.,  and  the  second  precipitate 
shall  be  collected  and  washed  on  the  filter  used  in  the  first  instance  if  this  is 
still  intact.     To  the  combined  filtrates  from  the  hydroxides  of  iron  and 
aluminum,  reduced  in  volume  if  need  be,  1  c.c.  of  ammonium  hydroxide 
shall  be  added,  the  solution  brought  to  boiling,  25  c.c.  of  a  saturated  solu- 
tion of  boiling  ammonium  oxalate  added,  and  the  boiling  continued  until 
the  precipitated  calcium  oxalate  has  assumed  a  well-defined  granular  form. 
The  precipitate  after  one  hour  shall  be  filtered  and  washed,  then  with  the 
filter  shall  be  placed  wet  in  a  platinum  crucible,  and  the  paper  burned  off 
over  a  small  flame  of  a  bunsen  burner;  after  ignition  it  shall  be  redissolved 
in  hydrochloric  acid  and  the  solution  diluted  to  100  c.c.     Ammonia  shall 
be  added  in  slight  excess,  and  the  liquid  boiled.     The  lime  shall  then  be 
reprecipitated  by  ammonium  oxalate,  allowed  to  stand  until  settled,  filtered, 
and  washed.     The  combined  filtrates  from  the  calcium  precipitates  shall  be 
acidified  with  hydrochloric  acid,  concentrated  on  the  steam  bath  to  about 
150  c.c.,  and  made  slightly  alkaline  with  ammonium  hydroxide,  boiled  and 
filtered  (to  remove  a  little  aluminum  and  iron  and  perhaps  calcium).     When 
cool,  10  c.c.  of  saturated  solution  of  sodium-ammonium-hydrogen  phosphate 
shall  be  added  with  constant  stirring.     When  the  crystalline  ammonium- 
magnesium  orthophosphate  has  formed,  ammonia  shall  be  added  in  moder- 
ate excess.     The  solution  shall  be  set  aside  for  several  hours  in  a  cool  place, 

1  Since  this  procedure  does  not  involve  the  determination  of  silica,  a  second  evaporation 
is  unnecessary. 


280 


MATERIALS  OF  CONSTRUCTION 


filtered,  and  washed  with  water  containing  2,5  per  cent  of  NH3.  The  pre- 
cipitate shall  be  dissolved  in  a  small  quantity  of  hot  hydrochloric  acid,  the 
solution  diluted  to  about  100  c.c.,  1  c.c.  of  a  saturated  solution  of  sodium- 


k-  .......  to  ......... 


j    | 


pl.SL. 


(<•  .....  -----  --  ^cw  ...................  ->) 

FIG.    1.  —  Le   Chatelier  apparatus. 

ammonium-hydrogen  phosphate  added,  and  ammonia  drop  by  drop,  with 
constant  stirring,  until  the  precipitate  is  again  formed  as  described  and  the 
ammonia  is  in  moderate  excess.  The  precipitate  shall  then  be  allowed  to 
stand  about  two  hours,  filtered,  and  washed  as  before.  The  paper  and 


APPENDIX  A  281 

contents  shall  be  placed  in  a  weighed  platinum  crucible,  the  paper  slowly 
charred,  and  the  resulting  carbon  carefully  burned  off.  The  precipitate 
shall  then  be  ignited  to  constant  weight  over  a  Meker  burner,  or  a  blast 
not  strong  enough  to  soften  or  melt  the  pyrophosphate.  The  weight  of 
magnesium  pyrophosphate  obtained  multiplied  by  72.5  gives  the  percentage 
of  magnesia.  The  precipitate  so  obtained  always  contains  some  calcium  and 
usually  small  quantities  of  iron,  aluminum,  and  manganese  as  phosphates. 

27.  Permissible  Variation. — A  permissible  variation  of  0.4  will  be  allowed, 
and  all  results  in  excess  of  the  specified  limit  but  within  this  permissible 
variation  shall  be  reported  as  5.00  per  cent. 

VIII.  DETERMINATION  OF  SPECIFIC  GRAVITY 

28.  Apparatus. — The  determination  of  specific  gravity  shall  be  made  with 
a  standardized  Le  Chatelier  apparatus  which  conforms  to  the  requirements 
illustrated  in  Fig.  1.     This  apparatus  is  standardized  by  the  United  States 
Bureau  of  Standards.     Kerosene  free  from  water,  or  benzine  not  lighter 
than  62  degrees  Baume,  shall  be  used  in  making  this  determination. 

29.  Method.— The  flask  shall  be  filled  with  either  of  these  liquids  to  a 
point  on  the  stem  between  zero  and  1  c.c.;  and  64  grams  of  cement,  of  the 
same  temperature  as  the  liquid,  shall  be  slowly  introduced,  taking  care 
that  the  cement  does  not  adhere  to  the  inside  of  the  flask  above  the  liquid 
and  to  free  the  cement  from  air  by  rolling  the  flask  in  an  inclined  position. 
After  all  the  cement  is  introduced,  the  level  of  the  liquid  will  rise  to  some 
division  of  the  graduated  neck ;  the  difference  between  readings  is  the  vol- 
ume displaced  by  64  grams  of  the  cement. 

The  specific  gravity  shall  then  be  obtained  from  the  formula 

Weight  of  cement  (grams) 

Specific  gravity  =  — — — — —   — —    — - 

Displaced  volume  (cubic  centimeters) 

30.  The  flask,  during  the  operation,  shall  be  kept  immersed  in  water,  in 
order  to  avoid  variations  in  the  temperature  of  the  liquid  in  the  flask, 
which  shall  not  exceed  0.5  degree  Centigrade.     The  results  of  repeated 
tests  should  agree  within  0.01. 

31.  The  determination  of  specific  gravity  shall  be  made  on  the  cement  as 
received;  if  it  falls  below  3.10,  a  second  determination  shall  be  made  after 
igniting  the  sample  as  described  in  Section  20. 

IX.  DETERMINATION  OF  FINENESS 

32.  Apparatus. — Wire   cloth  for  standard   sieves  for  cement  shall  be 
woven  (not  twilled)  from  brass,  bronze,  or  other  suitable  wire,  and  mounted 
without  distortion  on  frames  not  less  than  \\%  in.  below  the  top  of  the  frame. 
The  sieve  frames  shall  be  circular,  approximately  8  in.  in  diameter,  and  may 
be  provided  with  a  pan  and  cover. 

33.  A  standard  No.  200  sieve  is  one  having  nominally  an  0.0029-in.  open- 
ing and  200  wires  per  inch  standardized  by  the  United  States  Bureau  of 
Standards,  and  conforming  to  the  following  requirements : 


282  MATERIALS  OF  CONSTRUCTION 

The  No.  200  sieve  should  have  200  wires  per  inch,  and  the  number  of 
wires  in  any  whole  inch  shall  not  be  outside  the  limits  of  192  to  208.  No 
opening  between  adjacent  parallel  wires  shall  be  more  than  0.0050  in.  in 
width.  The  diameter  of  the  wire  should  be  0.0021  in.  and  the  average 
diameter  shall  not  be  outside  the  limits  0.0019  to  0.0023  in.  The  value  of 
the  sieve  as  determined  by  sieving  tests  made  in  conformity  with  the  stand- 
ard specification  for  these  tests  on  a  standardized  cement  which  gives  a 
residue  of  25  to  20  per  cent  on  the  No.  200  sieve,  or  on  other  similarly  graded 
material,  shall  not  show  a  variation  of  more  than  1.5  per  cent  above  or 
below  the  standards  maintained  at  the  Bureau  of  Standards. 

34.  Method. — The  test  shall  be  made  with  50  grams  of  cement.  The 
sieve  shall  be  thoroughly  clean  and  dry.  The  cement  shall  be  placed  on 
the  No.  200  sieve,  with  pan  and  cover  attached,  if  desired,  and  shall  be  held 
in  one  hand  in  a  slightly  inclined  position  so  that  the  sample  will  be  well  dis- 
tributed over  the  sieve,  at  the  same  time  gently  striking  the  side  about  150 
times  per  minute  against  the  palm  of  the  other  hand  on  the  upstroke.  The 
sieve  shall  be  turned  every  25  strokes  about  one-sixth  of  a  revolution  in 
the  same  direction.  The  operation  shall  continue  until  not  more  than  0.05 
gram  passes  through  in  1  minute  of  continuous  sieving.  The  fineness  shall 
be  determined  from  the  weight  of  the  residue  on  the  sieve  expressed  as  a 
percentage  of  the  weight  of  the  original  sample. 

36.  Mechanical  sieving  devices  may  be  used,  but  the  cement  shall  not 
be  rejected  if  it  meets  the  fineness  requirement  when  tested  by  the  hand 
method  described  in  Section  34. 


X.  MIXING  CEMENT  PASTES  AND  MORTARS 

36.  Method. — The    quantity   of   dry  material  to  be  mixed  at  one  time 
shall  not  exceed  1,000  grams  nor  be  less  than  500  grams.     The  proportions 
of  cement  or  cement  and  sand  shall  be  stated  by  weight  in  grams  of  the  dry 
materials;  the  quantity  of  water  shall  be  expressed  in  cubic  centimeters 
(1  c.c.  of  water  =  1  gram).     The  dry  materials  shall  be  weighed,  placed 
upon  a  non-absorbent  surface,  thoroughly  mixed  dry  if  sand  is  used,  and 
a  crater  formed  in  the  center,  into  which  the  proper  percentage  of  clean 
water  shall  be  poured;  the  material  on  the  outer  edge  shall  be  turned  into 
the  crater  by  che  aid  of  a  trowel.     After  an  interval  of  ^  minute  for  the 
absorption  of  the  water  the  operation  shall  be  completed  by  continuous, 
vigorous  mixing,  squeezing,  and  kneading  with  the  hands  for  at  least  1 
minute.1     During  the  operation  of  mixing,  the  hands  should  be  protected 
by  rubber  gloves. 

37.  The  temperature  of  the  room  and  the  mixing  water  shall  be  main- 
tained as  nearly  as  practicable  at  21  degrees  Centigrade  (70  degrees  Fahren- 
heit). 

1  In  order  to  secure  uniformity  in  the  results  of  tests  for  the  time  of  setting  and  tensile 
strength  the  manner  of  mixing  above  described  should  be  carefully  followed.  At  least  one 
minute  is  necessary  to  obtain  the  desired  plasticity  which  is  not  appreciably  affected  by 
continuing  the  mixing  for  several  minutes.  The  exact  time  necessary  is  dependent  upon 
the  personal  equation  of  the  operator.  The  error  in  mixing  should  be  on  the  side  of  over- 
mixing. 


APPENDIX  A 
XI.  NORMAL  CONSISTENCY 


283 


38.  Apparatus. — The  Vicat  apparatus  consists  of  a  frame  A  (Fig.  2)  bear- 
ing a  movable  rod  B,  weighing  300  grams,  one  end  C  being  1  cm.  in  diameter 
for  a  distance  of  6  cm.,  the  other  having  a  removable  needle  D,  1  mm.  in 
diameter,  6  cm.  long.  The  rod  is  reversible,  and  can  be  held  in  any  desired 
position  by  a  screw  E,  and  has  midway  between  the  ends  a  mark  F  which 


\B 


FIG.  2. — Vicat  apparatus. 


moves  under  a  scale  (graduated  to  millimeters)  attached  to  the  frame  A. 
The  paste  is  held  in  a  conical,  hard -rubber  ring  G,  7  cm.  in  diameter  at  the 
base,  4  cm.  high,  resting  on  a  glass  plate  H  about  10  cm.  square. 

39.  Method. — In  making  the  determination,  500  grams  of  cement,  with 
a  measured  quantity  of  water,  shall  be  kneaded  into  a  paste,  as  described 
in  Section  36,  and  quickly  formed  into  a  ball  with  the  hands,  completing 
the  operation  by  tossing  it  six  times  from  one  hand  to  the  other,  maintained 
about  6  in.  apart;  the  ball  resting  in  the  palm  of  one  hand  shall  be  pressed 
into  the  larger  end  of  the  rubber  ring  held  in  the  other  hand,  completely 
filling  the  ring  with  paste ;  the  excess  at  the  larger  end  shall  then  be  removed 
by  a  single  movement  of  the  palm  of  the  hand ;  the  ring  shall  then  be  placed 
on  its  larger  end  on  a  glass  plate  and  the  excess  paste  at  the  smaller  end 


284 


MATERIALS  OF  CONSTRUCTION 


sliced  off  at  the  top  of  the  ring  by  a  single  oblique  stroke  of  a  trowel  held  at 
a  slight  angle  with  the  top  of  the  ring.  During  these  operations  care  shall 
be  taken  not  to  compress  the  paste.  The  paste  confined  in  the  ring,  resting 
on  the  plate,  shall  be  placed  under  the  rod,  the  larger  end  of  which  shall  be 
brought  in  contact  with  the  surface  of  the  paste;  the  scale  shall  be  then  read, 
and  the  rod  quickly  released.  The  paste  shall  be  of  normal  consistency 
when  the  rod  settles  to  a  point  10  mm.  below  the  original  surface  in  %  min- 
ute after  being  released.  The  apparatus  shall  be  free  from  all  vibrations 
during  the  test.  Trial  pastes  shall  be  made  with  varying  percentages  of 
water  until  the  normal  consistency  is  obtained.  The  amount  of  water 
required  shall  be  expressed  in  percentage  by  weight  of  the  dry  cement. 

40.  The  consistency  of  standard  mortar  shall  depend  on  the  amount  of 
water  required  to  produce  a  paste  of  normal  consistency  from  the  same 
sample  of  cement.  Having  determined  the  normal  consistency  of  the 
sample,  the  consistency  of  standard  mortar  made  from  the  same  sample 
shall  be  as  indicated  in  Table  I,  the  values  being  in  percentage  of  the  com- 
bined dry  weights  of  the  cement  and  standard  sand. 


TABLE  I. — PERCENTAGE  OF  WATER  FOR  STANDARD  MORTARS 


Percentage  of 
water  for  neat 

Percentage  of 
water  for  one 

Percentage  of 
water  for  neat 

Percentage  of 
water  for  one 

cement  paste 
of  normal 

cement,  three 
standard  Ottawa 

cement  paste 
of  normal 

cement,  three 
standard  Ottawa 

consistency 

sand 

consistency 

sand 

15 

9.0 

23 

10.3 

16 

9.2 

24 

10.5 

17 

9.3 

25 

10.7 

18 

9.5 

26 

10  8 

19 

9.7 

27 

11.0 

20 

9.8 

28 

11.2 

21 

10.0 

29 

11.3 

22 

10.2 

30 

11.5 

XII.  DETERMINATION  OF  SOUNDNESS1 

41.  Apparatus. — A  steam  apparatus,  which  can  be  maintained  at  a  tem- 
perature between  98  and  100  degrees  Centigrade,  or  one  similar  to  that 
shown  in  Fig.  3,  is  recommended.  The  capacity  of  this  apparatus  may 
be  increased  by  using  a  rack  for  holding  the  pats  in  a  vertical  or  inclined 
position. 

1  Unsoundness  is  usually  manifested  by  change  in  volume  which  causes  distortion,  crack- 
ing, checking,  or  disintegration. 

Pats  improperly  made  or  exposed  to  drying  may  develop  what  are  known  as  shrinkage 
cracks  within  the  first  24  hours  and  are  not  an  indication  of  unsoundness.  These  conditions 
are  illustrated  in  Fig.  4. 

The  failure  of  the  pats  to  remain  on  the  glass  or  the  cracking  of  the  glass  to  which  the 
pats  are  attached  does  not  necessarily  indicate  unsoundness. 


APPENDIX  A 


285 


••••2/  T- 


A 

t*"  i 

TT  — 

r" 

\ 

~*         c 

/,  K£ 

0 

1 

u 

V 

o 

0 

•I1""' 

c 

0 

•  c 
*      C  3 

q_ 

^ 

J^-S 

E 

^>    a  i 

° 

ft 

io 

10  5!  M 

C 

1 

Q.^ 

0 

o 

H 

0 

, 

0 

•S 

GO 

JB 

\ 

-*_      3 

\[ 

J  w 

\_ 

^_ 

/ 

v 

\ 

*evj         g 

^H     h 


«! 


/ 


\ 


W<N;,#    ^ 


286 


MATERIALS  OF  CONSTRUCTION 


APPENDIX  A 


287 


42.  Method. — A  pat  from  cement  paste  of  normal  consistency  about  3  in. 
in  diameter,  ^  in.  thick  at  the  center,  and  tapering  to  a  thin  edge,  shall  be 
made  on  clean  glass  plates  about  4  in.  square,  and  stored  in  moist  air  for 
24  hours.     In  molding  the  pat,  the  cement  paste  shall  first  be  flattened  on 
the  glass  and  the  pat  then  formed  by  drawing  the  trowel  from  the  outer 
edge  toward  the  center. 

43.  The  pat  shall  then  be  placed  in  an  atmosphere  of  steam  at  a  temper- 
ature between  98  and  100  degrees  Centigrade  upon  a  suitable  support  1  in. 
above  boiling  water  for  5  hours. 

44.  Should  the  pat  leave  the  plate,  distortion  may  be  detected  best  with 
a  straight  edge  applied  to  the  surface  which  was  in  contact  with  the  plate. 

XIII.  DETERMINATION  OF  TIME  OF  SETTING 

46.  The  following  are  alternate  methods,  either  of  which  may  be  used  as 
ordered : 


(a)  Pat  with  top  surface  flattened  for  determining  time  of  setting  by  Gillmore  method. 


FIG.  5. — (6)  Gillmore  needles. 


46.  Vicat  Apparatus. — The  time  of  setting  shall  be  determined  with  the 
Vicat  apparatus  described  in  Section  38  (see  Fig.  2). 

47.  Vicat  Method. — A  paste  of  normal  consistency  shall  be  molded  in  the 
hard-rubber  ring  G  as  described  in  Section  39,  and  placed  under  the  rod  B, 
the  smaller  end  of  which  shall  then  be  carefully  brought  in  contact  with 


288  MATERIALS  OF  CONSTRUCTION 

the  surface  of  the  paste,  and  the  rod  quickly  released.  The  initial  set  shall 
be  said  to  have  occurred  when  the  needle  ceases  to  pass  a  point  5  mm. 
above  the  glass  plate  in  3^  minute  after  being  released;  and  the  final  set, 
when  the  needle  does  not  sink  visibly  into  the  paste.  The  test  pieces  shall 
be  kept  in  moist  air  during  the  test.  This  may  be  accomplished  by  placing 
them  on  a  rack  over  water  contained  in  a  pan  and  covered  by  a  damp  cloth, 
kept  from  contact  with  them  by  means  of  a  wire  screen;  or  they  may  be 
stored  in  a  moist  closet.  Care  shall  be  taken  to  keep  the  needle  clean,  as 
the  collection  of  cement  on  the  sides  of  the  needle  retards  the  penetration, 
while  cement  on  the  point  may  increase  the  penetration.  The  time  of 
setting  is  affected  not  only  by  the  percentage  and  temperature  of  the  water 
used  and  the  amount  of  kneading  the  paste  receives,  but  by  the  temperature 
and  humidity  of  the  air;  and  its  determination  is,  therefore,  only  approximate. 

48.  Gillmore  Needles. — The  time  of  setting  shall  be  determined  by  the 
Gillmore  needles.     The  Gillmore  needles  should  preferably  be  mounted  as 
shown  in  Fig.  5  (6). 

49.  Gillmore  Method. — The  time  of  setting  shall  be  determined  as  fol- 
lows: A  pat  of  neat  cement  paste  about  3  in.  in  diameter  and  %  in.  in  thick- 
ness with  a  flat  top  (Fig.  5  (a)),  mixed  to  a  normal  consistency,  shall  be 
kept  in  moist  air  at  a  temperature  maintained  as  nearly  as  practicable  at 
21  degrees  Centigrade  (70  degrees  Fahrenheit).     The  cement  shall  be  con- 
sidered to  have  acquired  its  initial  set  when  the  pat  will  bear,  without 
appreciable  indentation,  the  Gillmore  needle  }-{2  in.  in  diameter,  loaded 
to  weigh  }£  Ib.     The  final  set  has  been  acquired  when  the  pat  will  bear, 
without  appreciable  indentation,  the  Gillmore  needle  3^4  in.  in  diameter, 
loaded  to  weigh  1  Ib.     In  making  the  test,  the  needles  shall  be  held  in  a 
vertical  position  and  applied  lightly  to  the  surface  of  the  pat. 

XIV.  TENSION  TESTS 

60.  Form  of  Test  Piece. — The  form  of  test  piece  shown  in  Fig.  6  shall 
be  used.     The  molds  shall  be  made  of  non-corroding  metal  and  have  suffi- 
cient material  in  the  sides  to  prevent  spreading  during  molding.     Gang 
molds  when  used  shall  be  of  the  type  shown  in  Fig.  7.     Molds  shall  be 
wiped  with  an  oily  cloth  before  using. 

61.  Standard  Sand. — The  sand  to  be  used  shall  be  natural  sand  from 
Ottawa,  111.,  screened  to  pass  a  No.  20  sieve  and  retained  on  a  No.  30  sieve. 
This  sand  may  be  obtained  from  the  Ottawa  Silica  Co.,  at  a  cost  of  3  cents 
per  pound,  f.o.b.  cars,  Ottawa,  111. 

62.  This  sand,  having  passed  the  No.  20  sieve,  shall  be  considered  standard 
when  not  more  than  5  grams  pass  the  No.  30  sieve  after  1  minute  con- 
tinuous sieving  of  a  500-gram  sample. 

53.  The  sieves  shall  conform  to  the  following  specifications: 
The  No.  20  sieve  shall  have  between  19.5  and  20.5  wires  per  whole  inch 
of  the  warp  wires  and  between  19  and  21  wires  per  whole  inch  of  the  shoot 
wires.     The  diameter  of  the  wire  should  be  0.0165  in.,  and  the  average 
diameter  shall  not  be  outside  the  limits  of  0.0160  and  0.0170  in. 

The  No.  30  sieve  shall  have  between  29.5  and  30.5  wires  per  whole   inch 
of  the  warp  wires  and  between  28.5  and  31.5  wires  per  whole  inch   of  the 


APPENDIX  A 


289 


shoot  wires.     The  diameter  of  the  wire  should  be  0.0110  in.,  and  the  average 
diameter  shall  not  be  outside  the  limits  0.0105  to  0.0115  in. 

54.  Molding. — Immediately  after  mixing,  the  standard  mortar  shall  be 
placed  in  the  molds,  pressed  in  firmly  with  the  thumbs,  and  smoothed  off 
with  a  trowel  without  ramming.  Additional  mortar  shall  be  heaped  above 
the  mold  and  smoothed  off  with  a  trowel;  the  trowel  shall  be  drawn  over 


FIG.   6. — Details  for  briquette. 


the  mold  in  such  a  manner  as  to  exert  a  moderate  pressure  on  the  material. 
The  mold  shall  then  be  turned  over  and  the  operation  of  heaping,  thumbing, 
and  smoothing  off  repeated. 

66.  Testing. — Tests  shall  be  made  with  any  standard  machine.  The 
briquettes  shall  be  tested  as  soon  as  they  are  removed  from  the  water. 
The  bearing  surfaces  of  the  clips  and  briquettes  shall  be  free  from  grains 
of  sand  or  dirt.  The  briquettes  shall  be  carefully  centered  and  the  load 
applied  continuously  at  the  rate  of  600  Ib.  per  minute. 

66.  Testing  machines  should  be  frequently  calibrated  in  order  to  deter- 
mine their  accuracy. 
19 


290  MATERIALS  OF  CONSTRUCTION 

67.  Faulty  Briquettes. — Briquettes  that  are  manifestly  faulty,  or  which 
give  strengths  differing  more  than  15  per  cent  from  the  average  value  of  all 


FIG.  7. — Gang  mold. 

test  pieces  made  from  the  same  sample  and  broken  at  the  same  period, 
shall  not  be  considered  in  determining  the  tensile  strength. 

XV.  STORAGE  OF  TEST  PIECES 

58.  Apparatus. — The  moist  closet  may  consist  of  a  soapstone,  slate,  or 
concrete  box,  or  a  wooden  box  lined  with  metal.  If  a  wooden  box  is  used, 
the  interior  should  be  covered  with  felt  or  broad  wicking  kept  wet.  The 
bottom  of  the  moist  closet  should  be  covered  with  water.  The  interior  of 
the  closet  should  be  provided  with  non-absorbent  shelves  on  which  to  place 
the  test  pieces,  the  shelves  being  so  arranged  that  they  may  be  withdrawn 
readily. 

69.  Methods. — Unless  otherwise  specified  all  test  pieces,  immediately 
after  molding,  shall  be  placed  in  the  moist  closet  for  from  20  to  24  hours. 

60.  The  briquettes  shall  be  kept  in  molds  on  glass  plates  in  the  moist 
closet  for  at  least  20  hours.     After  24  hours  in  moist  air  the  briquettes 
shall  be  immersed  in  clean  water  in  storage  tanks  of  non-corroding  material. 

61.  The  air  and  water  shall  be  maintained  as  nearly  as  practicable  at  a 
temperature  of  21  degrees  Centigrade  (70  degrees  Fahrenheit). 


APPENDIX  B 
AMERICAN  SOCIETY  FOR  TESTING  MATERIALS 

PHILADELPHIA,  PA.,  U.  S.  A. 

AFFILIATED   WITH   THE 

INTERNATIONAL  ASSOCIATION  FOR  TESTING  MATERIALS 

STANDARD  SPECIFICATIONS 

FOR 
STRUCTURAL  STEEL  FOR  BUILDINGS 

Serial  Designation :  A  9-16 

These  specifications  are  issued  under  the  fixed  designation  A  9;  the  final 
number  indicates  the  year  of  original  adoption  as  standard,  or  in  the  case 
of  revision,  the  year  of  last  revision. 

ADOPTED,  1901;  REVISED,  1909,  1913,  1914,  1916 


In  view  of  the  abnormal  difficulty  in  obtaining  materials  in  time 
of  war,  the  rejection  limits  for  sulphur  in  all  steels  and  for  phos- 
phorus in  acid  steels  shall  be  raised  0.01  per  cent  above  the 
values  given  in  these  specifications.  This  shall  be  effective  during 
the  period  of  the  war  and  until  otherwise  ordered  by  the  Society. 


I.  MANUFACTURE 

1.  Process. — (a)  Structural  steel,  except  as  noted  in  Paragraph  (6),  may 
be  made  by  the  bessemer  or  the  open-hearth  process. 

(6)  Rivet  steel,  and  steel  for  plates  or  angles  over  %  in.  in  thickness 
which  are  to  be  punched,  shall  be  made  by  the  open-hearth  process. 

II.  CHEMICAL  PROPERTIES  AND  TESTS 

2.  Chemical    Composition. — The   steel   shall   conform   to    the   following 
requirements  as  to  chemical  composition : 

STRUCTURAL  STEEL,  RIVET  STEEL, 

PER  CENT  PER  CENT 

J  Bessemer Not  over  0 . 10 

18  \  Open-hearth .  .    .   Not  over  0 . 06  Not  over  0 . 06 

Sulphur Not  over  0 . 045 

291 


292 


MATERIALS  OF  CONSTRUCTION 


3.  Ladle  Analyses. — An  analysis  of  each  melt  of  steel  shall  be  made  by 
the  manufacturer  to  determine  the  percentages  of  carbon,  manganese,  phos- 
phorus, and  sulfur.     This  analysis  shall  be  made  from  a  test  ingot  taken 
during  the  pouring  of  the  melt.     The  chemical  composition  thus  determined 
shall  be  reported  to  the  purchaser  or  his  representative,  and  shall  conform 
to  the  requirements  specified  in  Section  2. 

4.  Check  Analyses. — Analyses  may  be  made  by  the  purchaser  from  fin- 
ished material  representing  each  melt.     The  phosphorus  and  sulfur  content 
thus  determined  shall  not  exceed  that  specified  in  Section  2  by  more  than 
25  per  cent. 

III.  PHYSICAL  PROPERTIES  AND  TESTS 

6.  Tension   Tests. — (a)  The   material   shall   conform    to    the   following 
requirements  as  to  tensile  properties: 


Properties  considered 

Structural  steel 

Rivet  steel 

Tensile    strength,     pounds     per 
square  inch  
Yield    point,    min.,    pounds    per 
square  inch 

.       55,000-65,000 
0  5  tensile  strength 

46,000-56,000 

1,400,000* 

1,400,000 

Elongation  in  2  in.,  min.,  per  cent 

Tensile  strength 
22 

Tensile  strength 

(b)  The  yield  point  shall  be  determined  by  the  drop  of  the  beam  of  the 
testing  machine. 

6.  Modifications  in  Elongation. — (a)  For  structural  steel  over  %  in.  in 
thickness,  a  deduction  of  1  from  the  percentage  of  elongation  in  8  in.  speci- 
fied in  Section  5  (a)  shall  be  made  for  each  increase  of  >£  in.  in  thickness 
above  %  in.,  to  a  minimum  of  18  per  cent. 

(b)  For  structural  steel  under  %6  in.  in  thickness,  a  deduction  of  2.5 
from  the  percentage  of  elongation  in  8  in.  specified  in  Section  5  (a)  shall  be 
made  for  each  decrease  of  Ho  in-  in  thickness  below  ^{Q  in. 

7.  Bend  Tests. — (a)  The  test  specimen  for  plates,  shapes,   arid  bars, 
except  as  specified  in  Paragraphs  (6)  and  (c),  shall  bend  cold  through  180 
degrees  without  cracking  on  the  outside  of  the  bent  portion,  as  follows: 
For  material  %  in.  or  under  in  thickness,  flat  on  itself;  for  material  over  % 
in.  to  and  including  1^  in.  in  thickness,  around  a  pin  the  diameter  of  which 
is  equal  to  the  thickness  of  the  specimen;  and  for  material  over  \%  in.  in 
thickness,  around  a  pin  the  diameter  of  which  is  equal  to  twice  the  thickness 
of  the  specimen. 

(b)  The  test  specimen  for  pins,  rollers,  and  other  bars,  when  prepared  as 
specified  in  Section  8  (e),  shall  bend  cold  through  180  degrees  around  a  1-in. 
pin  without  cracking  on  the  outside  of  the  bent  portion. 


See  Section  6. 


APPENDIX  B 


293 


(c)  The  test  specimen  for  rivet  steel  shall  bend  cold  through  180  degrees 
flat  on  itself  without  cracking  on  the  outside  of  the  bent  portion. 

8.  Test  Specimens. — (a,  Tension  and  bend  test  specimens  shall  be 
taken  from  rolled  steel  in  the  condition  in  which  it  comes  from  the  rolls, 
except  as  specified  in  Paragraph  (6). 

(6)  Tension  and  bend  test  specimens  for  pins  and  rollers  shall  be  taken 
from  the  finished  bars,  after  annealing  when  annealing  is  specified. 

./I 


.  i'J 

i  i  ! 

u^'ij*-  /*4<«*.4^*i 

I    j*......'*-.....,!    ' 


-About  16' 


FIG.   1. — Tension  and  bend  test  specimen. 


(c)  Tension  and  bend  test  specimens  for  plates,  shapes,  and  bars,  except 
as  specified  in  Paragraphs  (d),  (e),  and  (/),  shall  be  of  the  full  thickness  of 
material  as  rolled;  and  may  be  machined  to  the  form  and  dimensions  shown 
in  Fig.  1,  or  with  both  edges  parallel 


Z'Gage  Length—  H 


The  GagtLengih.  Parallel  Portions  and  Filleh  shall  bat  Show, 
but  tht  Endt  may  b«  of  any  Form  which  will  Fit  the  Ho/dery  of 
ffit  Testing  Machine. 

FIG.   2. — Tension   test   specimen. 


(d)  Tension  and  bend  test  specimens  for  plates  over  1^  in.  in  thickness 
may  be  machined  to  a  thickness  or  diameter  of  at  least  %  in.  for  a  length  of 
at  least  9  in. 

(e)  Tension  test  specimens  for  pins,  rollers,  and  bars  over  1^  in.  in  thick- 
ness or  diameter  may  conform  to  the  dimensions  shown  in  Fig.  2.     In  this 
case,  the  ends  shall  be  of  a  form  to  fit  the  holders  of  the  testing  machine  in 
such  a  way  that  the  load  shall  be  axial.     Bend  test  specimens  may  be  1  by 
H  in-  in  section.     The  axis  of  the  specimen  shall  be  located  at  any  point 
midway  between  the  center  and  surface  and  shall  be  parallel  to  the  axis  of 
the  bar. 

(/)  Tension  and  bend  test  specimens  for  rivet  steel  shall  be  of  the  full- 
size  section  of  bars  as  rolled. 


294  MATERIALS  OF  CONSTRUCTION 

9.  Number  of  Tests. — (a)  One  tension  and  one  bend  test  shall  be  made 
from  each  melt;  except  that  if  material  from  one  melt  differs  %  in.  or  more 
in  thickness,  one  tension  and  one  bend  test  shall  be  made  from  both  the 
thickest  and  the  thinnest  material  rolled. 

(6)  If  any  test  specimen  shows  defective  machining  or  develops  flaws, 
it  may  be  discarded  and  another  specimen  substituted. 

(c)  If  the  percentage  of  elongation  of  any  tension  test  specimen  is  less 
than  that  specified  in  Section  5  (a,  and  any  part  of  the  fracture  is  more  than 
%  in.  from  the  center  of  the  gage  length  of  a  2-in.  specimen  or  is  outside 
the  middle  third  of  the  gage  length  of  an  8-in.  specimen,  as  indicated  by 
scribe  scratches  marked  on  the  specimen  before  testing,  a  retest  shall  be 
allowed. 

IV.  PERMISSIBLE  VARIATIONS  IN  WEIGHT  AND  THICKNESS 

10.  Permissible  Variations. — The  cross-section  or  weight  of  each  piece 
of  steel  shall  not  vary  more  than  2.5  per  cent  from  that  specified;  except  in 
the  case  of  sheared  plates,  which  shall  be  covered  by  the  following  permissi- 
ble variations.     One  cubic  inch  of  rolled  steel  is  assumed  to  weigh  0.2833  Ib. 

(a)  When  Ordered  to  Weight  per  Square  Foot. — The  weight  of  each  lot1  in 
each  shipment  shall  not  vary  from  the  weight  ordered  more  than  the  amount 
given  in  Table  I. 

(b)  When  Ordered  to  Thickness. — The  thickness  of  each   plate  shall  not 
vary  more  than  0.01  in.  under  that  ordered. 

The  overweight  of  each  lot2  in  each  shipment  shall  not  exceed  the  amount 
given  in  Table  II. 

V.  FINISH 

11.  Finish. — The  finished  material  shall  be  free  from  injurious  defects 
and  shall  have  a  workmanlike  finish. 

VI.  MARKING 

12.  Marking. — The  name  or  brand  of  the  manufacturer  and  the  melt 
number  shall  be  legibly  stamped  or  rolled  on  all  finished  material,  except 
that  rivet  and  lattice  bars  and  other  small  sections  shall,  when  loaded  for 
shipment,    be    properly    separated    and    marked    for    identification.     The 
identification  marks  shall  be  legibly  stamped  on  the  end  of  each  pin  and 
roller.     The  melt  number  shall  be  legibly  marked,  by  stamping  if  practica- 
ble, on  each  test  specimen. 

VII.  INSPECTION  AND  REJECTION 

13.  Inspection. — The  inspector  representing    the    purchaser    shall  have 
free   entry,   at  all  times  while   work  on  the    contract    of  the  purchaser  is 

1  The  term  "lot"  applied  to  Table  I  means  all  of  the  plates  of  each  group  width  and  group 
weight. 

2  The  term  "lot"  applied  to  Table  II  means  all  of  the  plates  of  each  group  width  and  group 
thickness. 


APPENDIX  R 


295 


il 

•8.9 


OJ 

2-3 


5* 


3* 


50   X 

2* 

00  C 


J3AQ 


J8AQ 


JSAQ 


J3AQ 


•rapo.! 


J9AQ 


japun 


J3AQ 


japna 


J3AQ 


japun 


n 


99999999 


OiOOOOiCOOC 


oooooooo 


-0000000000000000 


.   .ooooicooo 
"   '•  os  06  1-  «o  "3  «3  ^  ^ 


.oooooooo 
•  eo  co  co  co  eo  eo  cc  n 


.   .   . oooooooo 
:  I  .'oot>.'<  " 


.     -OOOOOOOO«5 


.     .OOO"5O»OO«OO 
'  "  CO  W 


.   .000000000 
'•    ICOCOCOCOCOCOCOCM'CM 


.t^tflOO^^COCOfN 


.  CO  CO  CO  CO  CO  <N  (N  (N  (N 


.  CO  iO  «5  Tjf  •*  CO  CO  <N  <N 


OOOOOO«O«O«5OO 


eocoeoeocoeo<NCMiN(N<N 


ooooooooooo 

CO  CO  CO  CO  CO  (N  CM*  (N  <N  <N  <N 


OOOO»C»CiCOOOO 


IO  TJ«  rj  co  CO  <N  (N  (N  <N  CM'  IN 


1999999 

•  «co»oo«coooo  : 


10  1    o  <N  10  t>-  O  »o  O  O 


t 

L 


§ 

3 

S 

XXXXXXKXW 

Ordered  tl 

§ 

i 
s 

^, 

^3^313^1° 

c  « 
—  > 

CM  O 

•   •   -oooooooo 

'.      '.  05  I-i  10'  CO  -<  OS  00  1^ 

co 
I 

CO  t, 
*""•  O 

r^ 

V 

> 

"S 

J 

CM     • 

co- 

X 

o  w 

i.s: 

•   •   -oooooooo 

IDERED  TO 

11 

i.s: 

•    •    -00000000 

•   •  •*"  CM'  d  os  06  1>^  «  ui 

& 

3-g 

•    •    -OOOOOOOiO 

1 

11 

I.2: 

•     -  OJ  O  OS  00  t^  5O  U5  TJ< 

g 

03  3 

10  s 

g-B 

•     -OOOOOOOiOO 

jj 

o 

II 
1! 

2  ® 

•     •  CM  O  OS  00  t>-  O  »O  •*  Tj< 

OVERWEl 

M-3 

o  «5 

oooooooo«oo»o 

^  CN  O  Os'  00  1^'  «  10"  TjJ  Tjl  CO 

3RMISSIBLE 

e  excess  in  a 
expr 

t>."3 

X 

i.sr 

ooooooo>oo>oo 
csocsooi^oio^^co'co' 

•a 

8-s 

00000000^00 

i—  i 
—  i 

g 

S 

*5*w*w*w 

fed 

ooooo»oo«oo«o>o 

5s 

- 

"     *     " 

i 

:::::::::!: 

Ordered  thic 

1 

1 

•  "o  "3  ~  "3  "S  "c  "o  "u  "o    ! 
•xxxxxxxxx    • 
•ovo«o>cevv    • 

.  «     «    «o             ; 
|222222222° 

296  MATERIALS  OF  CONSTRUCTION 

being  performed,  to  all  parts  of  the  manufacturers'  works  which  concern  the 
manufacture  of  the  material  ordered.  The  manufacturer  shall  afford  the 
inspector,  free  of  cost,  all  reasonable  facilities  to  satisfy  him  that  the  mate- 
rial is  being  furnished  in  accordance  with  these  specifications.  All  tests 
(except  check  analyses)  and  inspection  shall  be  made  at  the  place  of  manu- 
facture prior  to  shipment,  unless  otherwise  specified,  and  shall  be  so 
conducted  as  not  to  interfere  unnecessarily  with  the  operation  of  the  works. 

14.  Rejection. — (a)  Unless  otherwise  specified,  any  rejection  based  on 
tests  made  in  accordance  with  Section  4  shall  be  reported  within  five  work- 
ing days  from  the  receipt  of  samples. 

(6)  Material  which  shows  injurious  defects  subsequent  to  its  acceptance 
at  the  manufacturers'  works  will  be  rejected,  and  the  manufacturer  shall 
be  notified. 

15.  Rehearing. — Samples  tested  in  accordance  with  Section  4,  which 
represent  rejected  material,  shall  be  preserved  for  two  weeks  from  the  date 
of  the  test  report.     In  case  of  dissatisfaction  with  the  results  of  the  tests, 
the  manufacturer  may  make  claim  for  a  rehearing  within  that  time. 


APPENDIX  C 

List  of  Standards  and  Tentative  Standards  of  the 
American  Society  for  Testing  Materials 


A.  FERROUS  METALS 

A    1-14.       Standard  Specifications  for  Carbon-steel  Rails. 

A  2-12.  Standard  Specifications  for  Open-hearth  Steel  Girder  and  High 
Tee  Rails. 

A    3-14.       Standard  Specifications  for  Low-carbon-steel  Splice  Bars. 

A    4-14.       Standard  Specifications  for  Medium-carbon-steel  Splice  Bars. 

A    5-14.       Standard  Specifications  for  High-carbon-steel  Splice  Bars. 

A    6-14.       Standard  Specifications  for  Extra-high-carbon-steel  Splice  Bars. 

A    7-16.       Standard  Specifications  for  Structural  Steel  for  Bridges. 

A    8-16.       Standard  Specifications  for  Structural  Nickel  Steel. 

A    9-16.       Standard  Specifications  for  Structural  Steel  for  Buildings. 

A  10-16.       Standard  Specifications  for  Structural  Steel  for  Locomotives. 

A  11-16.       Standard  Specifications  for  Structural  Steel  for  Cars. 

A  12-16.       Standard  Specifications  for  Structural  Steel  for  Ships. 

A  13-14.       Standard  Specifications  for  Rivet  Steel  for  Ships. 

A  14-16.  Standard  Specifications  for  Carbon-steel  Bars  for  Railway 
Springs. 

A  15-14.  Standard  Specifications  for  Billet-steel  Concrete  Reinforcement 
Bars. 

A  16-14.  Standard  Specifications  for  Rail-steel  Concrete  Reinforcement 
Bars. 

A  17-18.  Standard  Specifications  for  Carbon-steel  and  Alloy-steel 
Blooms,  Billets,  and  Slabs  for  Forgings. 

A  18-18.  Standard  Specifications  for  Carbon-steel  and  Alloy-steel 
Forgings. 

A  19-18.  Standard  Specifications  for  Quenched  and  Tempered  Carbon- 
steel  Axles,  Shafts,  and  Other  Forgings  for  Locomotives  and 
Cars. 

A  20-16.  Standard  Specifications  for  Carbon-steel  Forgings  for  Loco- 
motives. 

A  21-18.  Standard  Specifications  for  Carbon-steel  Car  and  Tender 
Axles. 

A  22-16.       Standard  Specifications  for  Cold-rolled  Steel  Axles. 

A  23.  Discontinued — Replaced  by  Specification  A  57. 

A  24.  Discontinued — Replaced  by  Specification  A  57. 

A  25-16.  Standard  Specifications  for  Wrought,  Solid  Carbon-steel  Wheels 
for  Electric  Railway  Service. 

A  26-16.        Standard  Specifications  for  Steel  Tires. 

297 


298 


MATERIALS  OF  CONSTRUCTION 


A  27-16.       Standard  Specifications  for  Steel  Castings. 

A  28-18.       Standard    Specifications   for   Lap-welded    and    Seamless    Steel 

Boiler  Tubes  for  Locomotives. 
A  29—18.       Standard    Specifications    for    Automobile    Carbon    and    Alloy 

Steels. 

A  30—18.       Standard  Specifications  for  Boiler  and  Firebox  Steel  for  Loco- 
motives. 

A  31-14.        Standard  Specifications  for  Boiler-rivet  Steel. 
A  32-14.       Standard  Specifications  for  Cold-drawn  Bessemer  Steel  Auto- 
matic Screw  Stock. 

A  33-14.        Standard  Methods  for  Chemical  Analysis  of  Plain  Carbon  Steel. 
A  34-18.        Standard  Tests  for  Magnetic  Properties  of  Iron  and  Steel. 
A  35-11.       Recommended  Practice  for  Annealing  of  Miscellaneous  Rolled 

and  Forged  Carbon-steel  Objects. 

A  36-14.       Recommended  Practice  for  Annealing  of  Carbon-steel  Castings. 
A  37-14.       Recommended  Practice  for  Heat  Treatment  of  Case-hardened 

Carbon-steel  Objects. 
A  38-18.       Standard   Specifications  for  Lap-welded    Charcoal-iron   Boiler 

Tubes  for  Locomotives. 

A  39-18.       Standard  Specifications  for  Staybolt  Iron. 
A  40-18.       Standard  Specifications  for  Engine-bolt  Iron. 
A  41-18.       Standard  Specifications  for  Refined  Wrought-iron  Bars. 
A  42-18.       Standard  Specifications  for  Wrought-iron  Plates. 
A  43-09.       Standard  Specifications  for  Foundry  Pig  Iron. 
A  44-04.       Standard  Specifications  for  Cast-iron  Pipe  and  Special  Castings. 
A  45-14.       Standard  Specifications  for  Cast-iron  Locomotive  Cylinders. 
A  46-05.       Standard  Specifications  for  Cast-iron  Car  Wheels. 
A  47-19.       Standard  Specifications  for  Malleable  Castings. 
A  48—18.       Standard  Specifications  for  Gray-iron  Castings. 
A  49-15.       Standard  Specifications  for  Quenched  High-carbon-steel  Splice 

Bars. 

A  50-16.       Standard  Specifications  for  Quenched  Carbon-steel  Track  Bolts. 
A  51-16.       Standard  Specifications  for  Quenched  Alloy-steel  Track  Bolts. 
A  52-12.       Standard  Specifications  for  Lap-welded  and  Seamless  Steel  and 

Wrought-iron  Boiler  Tubes  for  Stationary  Service. 
A  53-18.       Standard  Specifications  for  Welded  Steel  Pipe. 
A  53-20  T.  Tentative  Specifications  for  Welded  Steel  Pipe. 
A  54-15.       Standard    Specifications    for    Cold-drawn    Open-hearth    Steel 

Automatic  Screw  Stock. 

A  55-15.       Standard  Methods  for  Chemical  Analysis  of  Alloy  Steels. 
A  56-18.       Standard  Specifications  for  Iron  and  Steel  Chain. 
A  57-16.       Standard     Specifications     for     Wrought,     Solid     Carbon-steel 

Wheels  for  Steam  Railway  Service. 
A  58-16.       Standard  Specifications  for  Carbon-steel  Bars  for  Vehicle  and 

Automobile  Springs. 
A  59-16.       Standard    Specifications    for    Silico-manganese-steel    Bars    for 

Automobile  and  Railway  Springs. 
A  60-16.       Standard   Specifications  for  Chrome-vanadium-steel   Bars  for 

Automobile  and  Railway  Springs. 


APPENDIX  C  299 

A  61-16.  Standard  Specifications  for  Helical  Steel  Springs  for  Railways. 
A  62-16.  Standard  Specifications  for  Elliptical  Steel  Springs  for  Railways. 
A  63-18.  Standard  Specifications  for  Quenched-and-tempered  Alloy-steel 

Axles,  Shafts,  and  Other  Forgings  for  Locomotives  and  Cars. 
A  64—16.       Standard  Methods  for  Sampling  and  Analysis  of  Pig  and  Cast 

Iron. 

A  65-18.       Standard  Specifications  for  Steel  Track  Spikes. 
A  66-18.       Standard  Specifications  for  Steel  Screw  Spikes. 
A  67-20  T.  Tentative  Specifications  for  Steel  Tie  Plates. 
A  68-18.       Standard    Specifications   for    Carbon-steel    Bars    for    Railway 

Springs  with  Special  Silicon  Requirements. 

A  69-18.       Standard  Specifications  for  Elliptical  Steel  Springs  for  Auto- 
mobiles. 
A  70-18  T.  Tentative    Specifications    for    Boiler    and    Firebox    Steel   for 

Stationary  Service. 

A  71-20  T.  Tentative  Specifications  for  Carbon  Tool  Steel. 
A  72-18.       Standard  Specifications  for  Welded  Wrought-iron  Pipe. 
A  73-18.       Standard   Specifications  for   Wrought-iron   Rolled   or   Forged 

Blooms  and  Forgings  for  Locomotives  and  Cars. 

A  74-18.       Standard  Specifications  for  Cast-iron  Soil  Pipe  and  Fittings. 
A  75.  Discontinued — Has  become  A  47. 

A  76-20  T.  Tentative  Specifications  for  Low-carbon-steel  Track  Bolts. 
A  77-20  T.  Tentative  Specifications  for  Electric  Cast-steel  Anchor  Chain. 
A  78-20  T.  Tentative  Specifications  for  Steel  Plates  for  Forge  Welding. 
A  79-19  T.  Tentative  Specifications  for  Extra  Refined  Wrought-iron  Bars. 
A  80-20  T.  Tentative  Specifications  for  Commercial  Bar  Steels. 
A  81-20  T.  Tentative    Definitions    of    Terms    Relating   to    Wrought-iron 

Specifications. 


B.  NON-FERROUS  METALS 

B    1-15.       Standard  Specifications  for  Hard-drawn  Copper  Wire. 

B    2-15.       Standard  Specifications  for  Medium  Hard-drawn  Copper  Wire. 

B    3-15.       Standard  Specifications  for  Soft  or  Annealed  Copper  Wire. 

B    4-13.       Standard  Specifications  for  Lake  Copper  Wire  Bars,   Cakes, 

Slabs,  Billets,  Ingots,  and  Ingot  Bars. 
B    5-13.       Standard   Specifications  for   Electrolytic    Copper  Wire   Bars, 

Cakes,  Slabs,  Billets,  Ingots,  and  Ingot  Bars. 
B    6-18.       Standard  Specifications  for  Spelter. 
B    7-14.       Standard  Specifications  for  Manganese-bronze  Ingots  for  Sand 

Castings. 
B    8-16.       Standard  Specifications  for  Bare  Concentric-lay  Copper  Cable: 

Hard,  Medium-hard,  or  Soft. 
B    9-16.       Standard  Specifications  for  High-strength  Bronze  Trolley  Wire, 

Round  and  Grooved :  40  and  65  per  cent  Conductivity. 
B  10-18.       Standard   Specifications  for  the  Alloy:  Copper,   88  per  cent; 

Tin,  10  per  cent;  Zinc,  2  per  cent. 
B  11—18.       Standard    Specifications    for    Copper   Plates    for  Locomotive 

Fireboxes. 


300  MATERIALS  OF  CONSTRUCTION 

B  12-18.  Standard  Specifications  for  Copper  Bars  for  Locomotive  Stay- 
bolts. 

B  13-18.       Standard  Specifications  for  Seamless  Copper  Boiler  Tubes. 

B  14-18.       Standard  Specifications  for  Seamless  Brass  Boiler  Tubes. 

B  15-18.       Standard  Specifications  for  Brass  Forging  Rod. 

B  16-18.  Standard  Specifications  for  Free-cutting  Brass  Rod  for  Use  in 
Screw  Machines. 

B  17-18  T.  Tentative  Specifications  for  Non-ferrous  Alloys  for  Railway 
Equipment  in  Ingots,  Castings,  and  Finished  Car  and 
Tender  Bearings. 

B  18-20  T.  Tentative  Methods  for  Chemical  Analysis  of  Alloys  of  Lead, 
Tin,  Antimony,  and  Copper. 

B  19-19.       Standard  Specifications  for  Cartridge  Brass. 

B  20-19.       Standard  Specifications  for  Cartridge  Brass  Disks. 

B  21-19  Standard  Specifications  for  Naval  Brass  Rods  for  Structural 
Purposes. 

B  22-18  T.  Tentative  Specifications  for  Bronze  Bearing  Metals  for  Turn- 
tables and  Movable  Railroad  Bridges. 

B  23-18  T.  Tentative  Specifications  for  White  Metal  Bearing  Alloys 
(known  commercially  as  " Babbitt  Metal"). 

B  24-20  T.  Tentative  Specifications  for  Aluminum  Ingots  for  Remelting 
and  for  Rolling. 

B  25-19  T.  Tentative  Specifications  for  Aluminum  Sheet. 

B  26-19  T.  Tentative  Specifications  for  Light  Aluminum  Casting  Alloys. 

B  27-19.       Standard  Methods  for  Chemical  Analysis  of  Manganese  Bronze. 

B  28-19.       Standard  Methods  for  Chemical  Analysis  of  Gun  Metal. 

B  29-20  T.  Tentative  Specifications  for  Pig  Lead. 

B  30-19  T.  Tentative  Specifications  for  Brass  Ingot  Metal  for  Sand  Cast- 
ings. 

B  31-19  T.  Tentative  Specifications  for  Bronze  Bearing  Metal  in  Ingot 
Form. 

B  32-19  T.  Tentative  Specifications  for  Solder  Metal. 

B  33-19  T.  Tentative  Specifications  for  Tinned  Soft  or  Annealed  Copper 
Wire  for  Rubber  Insulation. 

B  34-20.       Standard  Methods  for  Battery  Assay  of  Copper. 

B  35-20.       Standard  Methods  for  Chemical  Analysis  of  Pig  Lead. 

B  36-20  T.  Tentative  Specifications  for  Sheet  High  Brass. 

B  37-20  T.  Tentative  Specifications  for  Aluminum  for  Use  in  the  Manu- 
facture of  Iron  and  Steel. 


C.  CEMENT,  LIME,  GYPSUM,  AND  CLAY  PRODUCTS 

C  1.  Discontinued — Replaced  by  Specifications  C  9  and  C  10. 

C  2.  Discontinued — Replaced  by  Specification  C  19. 

C  3.  Discontinued — Replaced  by  Specification  C  19. 

C  4-16.  Standard  Specifications  for  Drain  Tile. 

C  5-15.  Standard  Specifications  for  Quicklime. 

C  6-15.  Standard  Specifications  for  Hydrated  Lime. 


APPENDIX  C  301 

C    6-19  T.  Tentative  Specifications  for  Masons'  Hydrated  Lime. 

C    7-15.       Standard  Specifications  for  Paving  Brick. 

C    8-15.       Standard  Definitions  of  Terms  Relating  to  Sewer  Pipe. 

C    9-21.       Standard  Specifications  and  Tests  for  Portland  Cement. 

C  9-16  T.  Tentative  Specifications  and  Tests  for  Compressive  Strength 
of  Portland-cement  Mortars. 

C  10-09.       Standard  Specifications  for  Natural  Cement. 

C  11-16  T.  Tentative  Definitions  of  Terms  Relating  to  the  Gypsum 
Industry. 

C  12-19.       Recommended  Practice  for  Laying  Sewer  Pipe. 

C  13-20.       Standard  Specifications  for  Clay  Sewer  Pipe. 

C  14-20.       Standard  Specifications  for  Cement-concrete  Sewer  Pipe. 

C  15-17  T.  Tentative  Specifications  for  Required  Safe  Crushing  Strengths 
of  Sewer  Pipe  to  Carry  Loads  from  Ditch  Filling. 

C  16-20.  Standard  Test  for  Refractory  Materials  under  Load  at  High 
Temperatures. 

C  17-19  T.  Tentative  Test  for  Slagging  Action  of  Refractory  Materials. 

C  18-20.  Standard  Methods  for  Ultimate  Chemical  Analysis  of  Refrac- 
tory Materials. 

C  18-20  T.  Tentative  Method  for  Ultimate  Chemical  Analysis  of  Chrome 
Ores  and  Chrome  Brick. 

C  19-18.  Standard  Specifications  for  Fire  Tests  of  Materials  and  Con- 
struction. 

C  20-20.  Standard  Test  for  Porosity  and  Permanent  Volume  Changes 
in  Refractory  Materials. 

C  21-20.       Standard  Specifications  for  Building  Brick. 

C  22-20  T.  Tentative  Specifications  for  Gypsum. 

C  23-20  T.  Tentative  Specifications  for  Calcined  Gypsum. 

C  24-20.       Standard  Test  for  Softening  Point  of  Fireclay  Brick. 

C  25-19  T.  Tentative  Methods  for  Chemical  Analysis  of  Limestone,  Lime, 
and  Hydrated  Lime. 

C  26-20  T.  Tentative  Methods  for  Tests  of  Gypsum  and  Gypsum  Products. 

C  27-20.       Standard  Definitions  for  Clay  Refractories. 

C  28-20  T.  Tentative  Specifications  for  Gypsum  Plasters. 

C  29-20  T.  Tentative  Test  for  Unit  Weight  of  Aggregate  for  Cement 
Concrete.  • 

C  30-20  T.  Tentative  Method  for  Determination  of  Voids  in  Fine  Aggregate 
for  Cement  Concrete. 

C  31-20  T.  Tentative  Methods  for  Making  and  Storing  Specimens  of 
Concrete  in  the  Field. 


D.  MISCELLANEOUS  MATERIALS 

D  1-15.       Standard   Specifications  for   Purity   of  Raw  Linseed  Oil  from 

North  American  Seed. 

D    2-08.       Standard  Test  for  Abrasion  of  Road  Material. 
D    3-18.       Standard  Test  for  Toughness  of  Rock. 
D    4-11.       Standard  Test  for  Soluble  Bitumen. 


302 


MATERIALS  OF  CONSTRUCTION 


D    5-16.       Standard  Test  for  Penetration  of  Bituminous  Materials. 

D  6-20.  Standard  Test  for  Loss  on  Heating  of  Oil  and  Asphaltic  Com- 
pounds. 

D  7-18.  Standard  Method  for  Making  a  Mechanical  Analysis  of  Sand 
or  Other  Fine  Highway  Material,  Except  Fine  Aggregates 
Used  in  Cement  Concrete. 

D  8-18.  Standard  Definitions  of  Terms  Relating  to  Materials  for  Roads 
and  Pavements. 

D    9-15.       Standard  Definitions  of  Terms  Relating  to  Structural  Timber. 

D  10-15.  Standard  Specifications  for  Yellow-pine  Bridge  and  Trestle 
Timbers. 

D  11-15.  Standard  Specifications  for  Purity  of  Boiled  Linseed  Oil  from 
North  American  Seed. 

D  12-16.       Standard  Specifications  for  Purity  of  Raw  Tung  Oil. 

D  13-15.        Standard  Specifications  for  Turpentine. 

D  13-20  T.  Tentative  Specifications  for  Turpentine. 

D  14-15.  Standard  Specifications  for  2%-in.  Cotton  Rubber-lined  Fire 
Hose  for  Private  Department  Use. 

D  15-15.       Standard  Methods  for  Testing  of  Cotton  Rubber-lined  Hose. 

D  16-15.       Standard  Definitions  of  Terms  Relating  to  Paint  Specifications. 

D  17-16.       Standard  Specifications  for  Foundry  Coke. 

D  18-16.  Standard  Method  for  Making  a  Mechanical  Analysis  of  Broken 
Stone  or  Broken  Slag,  except  Aggregates  Used  in  Cement 
Concrete. 

D  19-16.  Standard  Method  for  Making  a  Mechanical  Analysis  of  Mix- 
tures of  Sand  or  Other  Fine  Material  with  Broken  Stone  or 
Broken  Slag,  except  Aggregates  Used  in  Cement  Concrete. 

D  20-18.  Standard  Method  for  Distillation  of  Bituminous  Materials 
Suitable  for  Road  Treatment. 

D  21-16.        Standard  Methods  for  Sampling  of  Coal. 

D  22-16.  Standard  Methods  for  Laboratory  Sampling  and  Analysis  of 
Coal. 

D  22-19  T.  Tentative  Method  for  Determination  of  Fusibility  of  Coal  Ash. 

D  23-20  T.  Tentative  Specifications  for  Structural  Douglas  Fir. 

D  24-20.  Standard  Specifications  for  Southern  Yellow-pine  Timber  to 
be  Creosoted. 

D  25-20.  Standard  Specifications  for  Southern  Yellow-pine  Piles  and 
Poles  to  be  Creosoted. 

D  26-18.  Standard  Specifications  for  2%-,  3-,  and  3j^-in.  Double- 
jacketed  Cotton  Rubber-lined  Fire  Hose  for  Public  Fire 
Department  Use. 

D  27-16  T.  Tentative  Specifications  for  Insulated  Wire  and  Cable:  30-Per 
Cent  Hevea  Rubber. 

D  28-17.        Standard  Tests  for  Paint  Thinners  Other  than  Turpentine. 

D  29-17.        Standard  Tests  for  Shellac. 

D  30-18.  Standard  Test  for  Determination  of  Apparent  Specific  Gravity 
of  Coarse  Aggregates. 

D  31.  Discontinued — Replaced  by  Method  D  39. 

D  32.  Discontinued— Replaced  by  Method  D  39. 


APPENDIX  C 


303 


D  33.  Discontinued — Replaced  by  Method  D  39. 

D  34-17.       Standard  Methods  for  Routine  Analysis  of  White  Pigments. 

D  35-18.  Standard  Form  of  Specifications  for  Certain  Commercial 
Grades  of  Broken  Stone. 

D  36-19.  Standard  Method  for  Determination  of  Softening  Point  of 
Bituminous  Materials  Other  than  Tar  Products  (Ring-and- 
Ball  Method). 

D  37-18.  Standard  Methods  for  Laboratory  Sampling  and  Analysis  of 
Coke. 

D  38-18.       Standard  Methods  for  Sampling  and  Analysis  of  Creosote  Oil. 

D  39-20.       Standard  General  Methods  for  Testing  Cotton  Fabrics. 

D  40-17  T.  Tentative  Specifications  for  Asphalt  for  Use  in  Damp-proofing 
and  Waterproofing. 

D  41-17  T.  Tentative  Specifications  for  Primer  for  Use  with  Asphalt  for 
Use  in  Damp-proofing  and  Waterproofing. 

D  42-17  T.  Tentative  Specifications  for  Coal-tar  Pitch  for  Use  in  Damp- 
proofing  and  Waterproofing. 

D  43-17  T.  Tentative  Specifications  for  Creosote  Oil  for  Priming  Coat 
with  Coal-tar  Pitch  for  Use  in  Damp-proofing  and  Water- 
proofing. 

D  44-20  T.  Tentative  Specifications  for  Wooden  Boxes,  Nailed  and  Lock- 
corner  Construction,  for  the  Shipment  of  Canned  Foods. 

D  45-17  T.  Tentative  Specifications  for  Canned  Foods  Boxes,  Wire-bound 
Construction. 

D  46-18.       Standard  Specifications  for  Air-line  Hose  for  Pneumatic  Tools. 

D  47-18.       Standard  Tests  for  Lubricants. 

D  47-  20.       Standard  Test  for  Viscosity  of  Lubricants. 

D  48-17  T.  Tentative  Tests  for  Molded  Insulating  Materials. 

D  49-18.       Standard  Methods  for  Routine  Analysis  of  Dry  Red  Lead. 

D  50-18.  Standard  Methods  for  Routine  Analysis  of  Yellow,  Orange, 
Red,  and  Brown  Pigments  containing  Iron  and  Manganese. 

D  51-18  T.  Tentative  Specifications  for  Foots  Permissible  in  Properly 
Clarified  Pure  Raw  Linseed  Oil  from  North  American  Seed. 

D  52-20.  Standard  Specifications  for  Wooden  Paving  Blocks  for  Exposed 
Pavements. 

D  53-20.  Standard  Specifications  for  Rubber  Belting  for  Power  Trans- 
mission. 

D  54-20.       Standard  Specifications  for  Steam  Hose. 

D  55-19.  Standard  Tests  for  Determination  of  Apparent  Specific  Gravity 
of  Sand,  Stone,  and  Slag  Screenings  and  Other  Fine  Non- 
bituminous  Highway  Materials. 

D  56-19.       Standard  Test  for  Flash  Point  of  Volatile  Paint  Thinners. 

D  57-20.  Standard  Specifications  for  Materials  for  Cement  Grout  Filler 
for  Brick  and  Stone-block  Pavements. 

D  58-20.  Standard  Specifications  for  Materials  for  Cement  Mortar  Bed 
for  Brick,  Stone-block,  and  Wood-block  Pavements. 

D  59-19  T.  Tentative  Specifications  for  Block  for  Granite-block  Pavements. 

D  60-20.  Standard  Specifications  for  Leader  Hose  for  Use  with  Pneu- 
matic Tools. 


304  MATERIALS  OF  CONSTRUCTION 

D  61-20.       Standard  Method  for  Determination  of  Softening  Point  of  Tar 

Products  (Cube-in-water  Method). 

D  62-20  T.  Tentative  Specifications  for  Workability  of  Concrete  for  Con- 
crete Pavements. 
D  63-20  T.  Tentative  Specifications  for  Commercial  Sizes  of  Broken  Stone 

and  Broken  Slag  for  Highway  Construction. 
D  64-20  T.  Tentative   Specifications  for   Commercial   Sizes   of   Sand   and 

Gravel  for  Highway  Construction. 

D  65-20  T.  Tentative  Specifications  for  Broken  Slag  for  Waterbound  Base. 
D  66-20  T.  Tentative  Specifications  for  Shovel-run  or  Crusher-run  Broken 

Slag  for  Waterbound  Base. 
D  67-20  T.  Tentative   Specifications  for   Natural  or   Artificial   Sand-clay 

Mixtures  for  Highway  Surfacing. 
D  68-20  T.  Tentative   General  Specifications  for   Wooden   Boxes,   Nailed 

and  Lock-corner  Construction. 

D  69-20  T.  Tentative  Specifications  for  Adhesive  Insulating  Tape. 
D  70-20  T.  Tentative  Test  for  Specific  Gravity  of  Road  Oils,  Road  Tars, 

Asphalt  Cements,  and  Soft  Tar  Pitches. 
D  71-20  T.  Tentative    Test   for    Specific    Gravity    of    Asphalts    and    Tar 

Pitches  Sufficiently  Solid  to  be  Handled  in  Fragments. 
D  72-20  T.  Tentative  Test  for  Quantity  of  Clay    and  Silt  in  Gravel  for 

Highway  Construction. 
D  73-20  T.  Tentative  Test  for  Quantity  of  Clay  in  Sand-clay,  Topsoil,  and 

Semi-gravel  for  Highway  Construction. 

D  74-20  T.   Tentative  Test  for  Quantity  of  Clay  and  Silt  in  Sand  for  High- 
way Construction. 
D  75-20  T.  Tentative  Methods  for  Sampling  of  Stone,  Slag,  Gravel,  Sand, 

and  Stone  Block  for  Use  as  Highway  Materials,  Including 

Some  Material  Survey  Methods. 
D  76-20  T.   Tentative  Methods  for  Testing  Textiles. 


E.  MISCELLANEOUS  SUBJECTS 
E  1-18.  Standard  Methods  for  Testing. 

E  2-20.  Standard    Definitions   and    Rules    Governing   the    Preparation   of 
Micrographs  of  Metals  and  Alloys. 


INDEX 


Aggregate,  coarse,  52 

fine,  37,  38,  51 
Air  furnace,  181 
Alloy  steels,  244 

aluminum  steel,  247 

chrome  steel,  247 

chromium-nickel  steel,  248 

chromium-vanadium  steel,  248 

classification  of,  244 

cobalt  steel,  247 

copper  steel,  248 

definitions  of,  244 

heat  treatment  of,  245 

manganese  steels,  246 

molybdenum  steel,  247 

nickel  steel,  246 

nickel-vanadium  steel,  249 

silicon  steel,  247 

tungsten-chromium-vanadium 
steel,  249 

tungsten,  steel,  247 

vanadium  steel,  247 
Alloys,  bearing  metal,  263 

fusible,  264 

miscellaneous,  265 
Alloys  of  aluminum,  262 

of  nickel,  263 

of  non-ferrous  metals,  259 

of    non-ferrous    metals,    corro- 
sion of,  265 

of  non-ferrous  metals  in  general, 

259 

Alpha  iron,  227 
Aluminum,  257 

alloys,  262 

bronze,  262 

copper  alloys,  262 

copper-tin  alloys,  262 

copper-zinc  alloys,  262 


Aluminum,  extraction  of,  257 

magnesium  alloys,  262 

plating,  253 

properties  of,  257 

steel,  247 

uses  of,  258 

zinc  alloys,  262 

American  Society  for  Testing 
Materials,  list  of  standards, 
297 

list  of  tentative  standards,  297 

standard  specifications  and  tests 
for   Portland  cement,   275 
Antimony,  259 
Asbestos,  268 

properties  of,  268 

uses  of,  268 
Asphalt  paints,  268 
Austenite,  227 


H 


Bauer  drill  test,  237 
Bearing  metal  alloys,  263 

composition  of,  264 

requisites  of,  264 
Belts,  273 

canvas,  274 

leather,  273 

rubber,  273 

splicing  of,  274 

steel,  274 
Beta  iron,  227 
Bismuth,  259 
Blast  furnace,  168 
259 

composition  of,  260 

definition  of,  260 

delta  metal,  261 

effect  of  adding  aluminum.  260 
lead,  260 


305 


20 


306 


INDEX 


Brasses,  manganese  bronze,   260 

properties  of,  260 

sterro-metal,    261 

strength  of,  261 

Tobin  bronze,  261 
Brick,  101 

absorption,  114 

acid,  109 

basic,  109 

bauxite,  110 

building,  101 

chromite,  110 

classification  of,  101 

clay  building,  102 

compressive    strength    of,    115 

definition  of,  101 

facing,  101 

fire,  101 

fireclay,  110 

ganister,  110 

general  properties  of,  114 

kilns,  106 

list  of  standards  and  tentative 
standards,  297 

modulus  of  elasticity,  116 

neutral,  110 

properties  of,  114 

requisites  of,  114 

sand-lime,  manufacture  of,  111 

shearing  strength  of,  116 

silica  firebrick,  110 

transverse  strength  of,  115 

veneer,  129 
Brick  masonry,  119,  127 

bond,  129 

cleaning,  131 

definitions,  119 

efflorescence,  133 

in  general,  127 

laying,  128 

mortar  for,  127 

pointing,  130 

properties  of,  131 

strength  of,  131 

waterproofing,  130 

working  load,  132 
Brinell  hardness  test,  237 
Bronzes,  261 


Bronzes,  aluminum,  262 
composition  of,  261 
definition  of,  261 
lead,  261 
phosphor,  261 
strength  of,  262 
Tobin,  261 
Building  stone,  89 
action  of  fire,  98 

of  frost,  97 

of  rain,  97 

of  smoke,  97 

of  wind,  97 
classification  of,  89 
cut  stone,  96 
cutting,  94 
durability  of,  96 
general,  89 
gneiss,  90 
granite,  90 
limestone,  91 
marble,  91 

mechanical  properties  of,  98 
properties  of,  96 
quarrying,  91 

explosives  used,  93 

hand  methods,  91 

machine  methods,  93 
sandstone,  91 
slate,  91 
strength  of,  99 
trap,  90 

Building  tile,  112 
absorption,  114 
compressive  strength  of,  115 
modulus  of  elasticity  of,  116 
shearing  strength  of,  116 
transverse  strength  of,  1 15 


Cadmium,  259 
Calcined  plaster,  1 
Canvas,  272 

belts,  274 
Cast  iron,  177 

arbitration  test  bar,  191 

blow  holes,  184 


INDEX 


307 


Cast  iron,  cementite,  185 
classification  of,  177 
coefficient  of  expansion  of,  192 
cold  shorts,  184 
composition  of,  184 
compressive  strength  of,  190 
constitution  of,  184 
cracks,  184 
defects,  184 
definitions  of,  177 
effect  of  aluminum,  188 

of  carbon,  185 

of  copper,  188 

of  manganese,  186 

of  phosphorus,  186 

of  silicon,  186 

of  sulphur,  186 

of  tin,  188 

of  titanium,  188 

of  vanadium,  188 
ferrite,  185 
fusibility  of,  192 
graphite,  185 
gray,  186 
malleable,  193 

annealing,  193 

compressive      strength       of, 
194 

definition  of,  193 

ductility  of,  194 

making  castings,  193 

properties  of,  194 

structure  of,  194 

tensile  strength  of,  194 

transverse  strength  of,  194 

uses  of,  194 

mechanical  properties  of,  188 
mottled,  186 
pearlite,  185 
physical  properties,  188 
rough  surfaces,  184 
sand-holes,  184 
seams,  184 

shearing  strength,  192 
shrinkage  in  cooling,  192 
specific  gravity,  192 
strength  in  general,  188 
tensile  strength,  189 


Cast  iron,  transverse  strength,  191 

uses  of,  192 

white,  186 

working  stresses,  192 
Cast  iron  manufacture,  178 

air  furnace,  181 

chills,  183 

cleaning  castings,  183 

cores,  181 

cupola,  179 

definition  of  founding,  181 

dry  sand  molds,  183 

foundry  work,  181 

green  sand  molds,  182 

loam  molds,  183 

materials,  178 

metal  molds,  183 

molding  sand,  182 

molds,  182 

patterns,  181 

pickling  castings,  184 

pouring  castings,  183 
Castings,  steel,  243 
Cement,  list  of  standards  and  tenta- 
tive standards,  300 

magnesia,  7 

miscellaneous,  6 

natural,  3 

plaster,  1 
Portland,  21 
Puzzolan,  6 
slag,  6 
Sorel,  7 
Cementing  materials,   classification 

of,  21 

Cementite,  185 
Chrome  steel,  247 
Chromium-nickel  steel,  248 
Chromium-vanadium  steel,  248 
Clay  building  brick,  102 

manufacture,  brick  kilns,  106 

burning  of  brick,  108 

hand  process,  102 

of  building  brick  102 

pressed-brick    machine    pro- 
cess, 106 

soft-mud     machine     process, 
103 


308 


INDEX 


Clay  building  brick,  manufacture, 

stiff-mud  process,  104 
the  clay,  102 
Clay  products,  101 

building  tile,  101,  112 

absorption,  114 

compressive  strength  of,  115 

modulus  of  elasticity  of,  116 

shearing  strength  of,  116 

transverse  strength  of,  116 

classification  of,  101 
definitions  of,  101 
drain  tile,  101,  112 

properties  of,  119 
list  of  standards  and  tentative 

standards,  300 
properties     of,     114 
sewer  pipe,  113 

properties  of,  118 
sewer  tile,  101 
terra  cotta,  101,  111 
Coarse  aggregate,  general,  52 
size,  52 

specific  gravity,  53 
specifications,  54 
voids,  53 

weight  per  cubic  foot,  53 
Cobalt  steel,  247 
Concrete,  abrasion,  82 
absorption,  82 

adhesive  strength  to  steel,   80 
bonding  new  to  old,  70 
coarse  aggregate,  52 
compressive  strength  of,  78 
consistency  of,  68 
contraction,  82 
definitions,  51 
deposition  of,  69 
effect    of    amount    of    mixing 
water,  75 

of  clay,  74 

of  dirt,  74 

of  grease  and  oil,  74 

of  lime,  74 

of  loam,  74 

of  mica,  74 

of  organic  matter,  74 

of  regaging,  74 


Concrete  effect  of  sugar,  74 

of  various  impurities,  74 

elastic  limit,  81 

expansion,  82 

factor  of  safety,  82 

forms  for,  69 

hardened,  effect  of  acids,  75 
of  alkali,  75 
of  fire,  75 

of  grease  and  oil,  75 
of  sea  water,  75 

impervious,  72 

effect  of  amount  of  cement,  72 
of  increasing  the  density,  72 
foreign  matter,  73 
surface  treatments,  73 
waterproofing  materials,  73 

material,  51 
cement,  51 
fine  aggregate,  51 
water,  51 

mixing,  66 
by  hand,  66 
by  machine,  68 

modulus  of  elasticity,  81 

placing,  69 

in  freezing  weather,  71 
under  water,  71 

plain,  51 

properties  of,  74 

proportioning,  55 

Abrams'  method,  60,  61 
by  standard  proportions,  55 
Edwards'         surface        area 

method,  65 
general  theory,  55 
maximum  density  test,  56 
mechanical  analysis,  57,  58 
quantities    of    materials    re- 
quired, 65 
reference  to  coarse  aggregate, 

56 
to  mixed   aggregate,   56 

rubble,  83 

shearing  strength,  80 

strength  in  general,  77 

surface  finish,  70 

tamping  of,  69 


INDEX 


309 


Concrete,  tensile  strength,  79 
transporting,  69 
transverse  strength,  79 
waterproofing  of,  72 
weight  per  cubic  foot,  82 
working  stresses,  82 
yield  of,  81 

Concrete  stone,  block,  and  brick,  84 
consistency,  85 
curing  and  aging,  86 
definitions,  84 
materials,  84 
mixing,  85 
molding,  85 
properties  of,  87 
proportions,  84 
surface  finishes,  86 
uses  of,  88 
Constantin,  263 
Copper,  255 

extracting  from  ores,  255 
properties  of,  255 
strength  of,  255 
uses  of,  256 
Copper  steel,  248 
Corrosion,     carbon-dioxide    theory, 

250 

definition  of,  249 
electrolytic   theory,    251 
moisture  theory,  251 
of   alloys,    non-ferrous   metals, 

265 

of  iron  and  steel,  249 
life  under,   250 
of  non-ferrous  metals,  265 
prevention    of,    by    aluminum 

plating,  253 

by  covering  with  asphalt,  252 
by   covering   with    concrete, 

252 

by  galvanizing,  252 
by  inoxidation  process,  253 
by  lead  plating,  253 
by  nickel  plating,  253 
by  painting,  251 
by  sheradizing,  253 
by  tin  plating,  253 
in  general,  251 


Corrosion,  theories  of,  250 

Cupola,  179 

Cut  stone,  classification,  95 

D 

Delta  metal,  261 
Drain  tile,  112 

properties  of,  117 


E 


Electric  furnace,  174,  217 
Electric   welding,   238 
Explosives  used  in  quarrying,  93 


Ferrite,  185 

Ferrous    metals,    list    of   standards 
and    tentative    standards, 
297 
Fine  aggregate,  for  plain  concrete,  51 

definition  of,  37 

specifications,  40 
Firebrick,  manufacture  of,  109 
Forms  for  concrete,  69 
Foundry  work,  181 
Fusible  alloys,  260 


Galvanized  wire,  standards  test  fo  r, 

253 

Galvanizing  of  iron  and  steel,  252 
Gamma  iron,  227 
German  silver,  263 
Glass,  268 

properties  of,  268 

uses  of,  268 

wire,  269 
Glue,  269 

properties  of,  269 

uses  of,  269 
Gneiss,  90 
Gold,  254 
Granite,  90 
Graphite,  185 
Gypsum,  1 


310 


INDEX 


Gypsum,  list  of  standards  and  ten- 
tative standards,    300 
plaster,  1 

calcined  plaster,  1 
cement  plaster,  1 
classification  of,  1 
definition  of,  1 
hard-finish  plaster,  1 
manufacture  of,  1 
plaster  of  Paris,  1 
properties  of,  2 
uses  of,  3 
products,  3 


H 


Hard-finish  plaster,  1 
Hollow  tile  masonry,  127,  133 
Hydrated  lime,  9,  12,  14 


I 


Inoxidation  process,  253 

Invar,  263 

Iron  carbide,  227 

Iron,  cast,  177 

Iron,  corrosion  of,  249 
life  under,  250 
galvanizing  of,  252 
general  classification,  177 
Howe's  classification,  177 
list  of  standards  and  tentative 

standards,  297 
malleable  cast,  193 
ores,  165 

preliminary  treatment,  166 
pig,  165 
wrought,  197 

Iron  ore  mining,  166 


Lead,  256 

extraction  of,  256 
properties  of,  256 
uses  of,  256 

Lead  bronze,  261 

Lead  plating,  253 

Leather,  271 


Leather,  classification  of,  271 
.properties  of,  271 
uses  of,  272 
Leather  belts,  273 
Leather,  rawhide,  272 
Lime,  9 

calcium,  9 

classification  of,  9 

definition  of,  9 

dolomite,  9 

high-calcium,  9 

hydrated,  9 

hydraulic,  9 

list  of  standards  and  tentative 

standards,    300 
magnesium,  9 
manufacture  of  hydrated  lime, 

12 

of  hydraulic  lime,  12 
of  quicklime,  9 

properties  of  hydrated  lime,  14 
of  hydraulic  lime,  14 
of  quicklime,  13 
quicklime,  9 
run-of-kiln,  9 
selected,  9 

slaking  quicklime,  16 
uses,  15 
Lime  kiln,  10 
Lime  mortars,  9,15 
definitions,  15 
materials,  15 
mixing,  17 
properties  of,  18 
proportioning,  17 
slaking  quicklime,  16 
uses  of,  19 
Limestone,  91 
Linseed  oil,  267 

Lumber,  artificial  seasoning,  147 
classification,  144 
common  rot,  151 
decay,  149 
defects  in,  145 
dry  rot,  150 
durability,  149 
inspection  of,  159 
natural  seasoning,  147 


INDEX 


311 


Lumber,  sawing,  144 
selection  of,  158 
shrinkage,  148 
wet  rot,  151 

M 

Magnalium,  262 
Magnesia  cement,  7 
Magnesium,  259 
Malleable  cast  iron,  193 
Manganese,  259 

bronze,  260 

properties  of,  260 
strength  of,  260 
Manganese  steel,  246 
Marble,  91 
Martensite,  227 
Masonry,  119 

Materials,  miscellaneous,  267 
Metals,    non-ferrous,    255 

alloys  of,  259 
Miscellaneous  cements,  6 
Mixing  of  concrete,  66 
Molybdenum  steel,  247 
Monel  metal,  263 
Mortar  for  brick  masonry,  127 

for  stone  masonry,  122 
Mortars,  lime,  9,  15 

N 

Natural  cement,  1,  3 

definition  of,  3 

manufacture  of,  4 

properties  of,  4 

uses  of,  6 
Nickel,  258 

extraction  of,  258 

properties  of,  258 

uses  of,  258 
Nickel  alloys,  263 

constantin,  263 

german  silver,  263 

invar,  263 

monel  metal,  263 

table  ware  alloy,  263 
Nickel  plating,  253 
Nickel  steel,  246 


Nickel-vanadium  steel,  249 
Non-ferrous  metals,  255 

alloys  of,  259 

corrosion  of,  265 

in  general,  255 

list    of    standards    and    tenta- 
tive standards,  299 


O 


Oils,  267 
Ore  mining,  166 
Ore  of  iron,  165 
Oxygen-acetylene 
238 


welding   process, 


Paints,  267 

asphalt,  268 

composition  of,  267 

drier,  267 

linseed  oil,  267 

solvent,  267 

stain,  267 

turpentine,  267 

vehicle  or  binder,  267 

white  lead,  267 

zinc  white,  267 
Paper,  272 

classification  of,  272 

manufacture  of,  272 
Paving  brick,  manufacture  of,  108 
Pearlite,  185,  227 
Pewter,  265 
Phosphor-bronze,  261 
Pig  iron,  165 

chemical  contents,  175 

classification  of,  175 

definition  of,  165 

uses  of,  176 
Pig  iron  manufacture,  168 

blast  furnace,  168 
accessories,  171 
operation,  172 

casting  pigs,  175 

electric  furnace,  174 


312 


INDEX 


Pig  iron  manufacture,  flux  used,  172 
fuel,  171 

hot  blast  stoves,  171 
slag,  174 
Pig  iron  ores,  165 
Plain  concrete,  51 
Plaster,  1 

common  lime,  19 
of  Paris,  1 
wall,  19 
Plasters,  1 
Platinum,  258 
Portland  cement,  21 

chemical  specifications,  275 
classification  of,  21 
definition  of,  21,  275 
manufacture   of  raw  materials, 

21 
standard    specifications    and 

tests  for,  275 
uses  of,  36 

Portland  cement  manufacture,  21 
adding  retarder,  30 
burning,  29 
crushing  materials,  25 
dry  process,  25 
drying  materials,  25 
fine  grinding  of  materials,  28 
flow  sheet,  23,  24,  31 
grinding  clinker,  30 

material,  26 

proportioning  raw  materials,  22 
wet  process,  32 
Portland  cement  mortars,  37 
abrasive  resistance,  48 
absorption,  48 
adhesive  strength,  47 
cement,  37 

compressive  strength,  46 
contraction.  48 
definition,  37 
effect    of    amount    of    mixing 

water,  44 

of  density  of  sand,  43 
of  size  of  sand,  43 
of   various    conditions,    44 

elements,  45 
materials,  37 


Portland  cement  mortars,  miscella- 
neous properties,  48 

mixing,  42 

permeability,  48 

properties,  43 

proportioning,  42 

sand,  37 

shearing  strength,  47 

strength  in  general,  43 

tensile  strength,  46 

transverse  strength,  47 

voids,  49 

water,  37 

weight,  49 
Portland  cement  properties,  32 

chemical  constitution,  32 
specifications,  32 

expansion,  48 

fineness,  35 

specific  gravity,  36 

soundness,  33 

strength,  34 

time  of  set,  35 
Portland  cement  specifications,  275 

fineness,  276 

inspection,  276 

marking,  276 

packages,  276 

rejection,  276 

soundness,  276 

specific  gravity,  275 

storage,  276 

tensile  strength,  276 

time  of  set,  276 
Portland  cement  tests,  277 

briquettes,  289 
molds,  290 

chemical  analysis,  277 

fineness,  281 

Gillmore  needles,  287 

insoluble  residue,  278 

Le  Chatelier  apparatus,  280 

loss  on  ignition,  277 

magnesia,  279 

mixing  cement  pastes,  282 
mortars,  282 

moist  closet,  290 

molding  briquettes,  289 


INDEX 


313 


Portland  cement  tests,  normal  con- 
sistency, 283 
Ottawa  sand,  288 
sampling,  277 
soundness,  284 

steam  apparatus,  284 
specific  gravity,  281 
standard  mortar,  284 
percentage  of  water,  284 
standard  sand,  288 

standard  sieves,  281 
storage  of  test  pieces,  290 
sulphuric  anhydride,  278 
tension,  288 
testing  briquettes,  289 
time  of  set,  287 
Vicat  apparatus,  283 
Properties  of  concrete,  74 
Proportioning  of  concrete,  55 
Puddling  furnace,  199 
Puzzolan  cement,  6 


Q 


Quicklime,  9,  13 


R 


Rawhide,  272 

Reverberatory  regenerative  furnace, 

213 

Riprap,  120 
Ropes,  272 

properties  of,  273 

wire,  273 
Rubber,  269 

belts,  273 

derivation  of,  269 

properties  of,  270 

uses  of,  271 

vulcanizing  of,  270 
Rubble  concrete,  83 


Sand,  37 

composition  of,  38 

for  Portland  cement  mortars,  37 

properties  of,  38 


Sand,  sieve  analysis,  38 

standard,  39 

substitutes  for,  39 
Sand-lime   bricks,   manufacture  of, 

111 

Sandstone,  91 
Sewer  pipe,  113 

properties  of,  118 
Sherardizing  of  iron  and  steel,  253 
Shore  scleroscope  test,  237 
Silicon  steel,  247 
Silver,  258 
Slag  cement,  6 
Slaking  quicklime,  16 
Slate,  91 
Solders,  265 
Sorbite,  227 
Sorel  cement,  7 
Special  steels,  243 
Specifications  for  structural  steel  for 

buildings,  291 
Standard  sand,  39 
Standards,    American    Society    for 
testing   materials,    list  of, 
297 
Steel,  207 

alpha  iron,  227 

aluminum,  247 

annealing,  explanation  of,  229 

austenite,  227 

beta  iron,  227 

Bauer  drill  test,  237 

Brinell  hardness  test,  237 

coefficient  of  expansion  of,  239 

classification,  207 
of  carbon  steels,  230 

cold  bending  test,  236 

compounds  of,  224 

compressive  strength  of,  233 

constitution  of,  224 

corrosion  of,  249 
life  under,  250 

critical  temperature,  226 

definitions,  207 

ductility  of,  236 

effect  of  alternating  stresses,  237 
of    annealing.    232 
of  carbon,  230 


314 


INDEX 


Steel,  effect  of  cold  working,  232 

of  combined  stresses,  235 

of  hardening,  232 

of  heat  treatment,  232 

of  hot  working,  232 

of  manganese,  232 

of  mechanical  working,  232 

of  phosphorus,  232 

of  repeated  stresses,  237 

of  silicon,  231 

of  sulphur,  231 
electric  welding,  238 
elongation  of,  233 
eutectic  solution,  225 
eutectoid  solution,  225 
fatigue  of,  237 
galvanizing  of,  254 
gamma  iron,  227 
general  classification,  177 
hardening,  explanation  of,  228 
hardness  of,  237 
Harvey ized  armor  plate,  224 
heat  treatment,  223 

annealing,  223 

case  hardening,  224 

hardening,  223 

tempering,  223 
Howe's  classification,  177 
hyper-eutectic  solution,  225 
hyper-eutectoid  solution,  225 
hypo-eutectic  solution,  225 
hypo-eutectoid  solution,  225 
iron  carbide,  227 
list  of  standards  and  tentative 

standards,  297 
magnetic  properties,  238 
manufacture  of,  208 
martensite,  227 
mechanical  properties  of,  229 
molybdenum,  247 
normal  constituents  of,  224 
oxygen-acetylene  welding  proc- 
ess, 238 
pearlite,  227 
physical  properties,  229 
properties  in  general,  229 
properties  of  rolled  carbon  steel, 
234 


Steel,  rapid  cooling  of,  227 
recalescence,  226 
resistance  to  impact,  235 
shearing  strength  of,  234 
Shore  scleroscope  test,  237 
silicon,  247 
slow  cooling,  227 
sorbite,  227 
specific  gravity  of,  239 
strength    formulas    for    carbon 

steels,  231 
structural  working  stresses  for, 

230 

structure  of,  224 
summarized   specifications   for, 

239 

tempering,  explanation  of,  228 
tensile  strength  of,  232 
thermit  process  for  welding,  238 
transverse  strength  of,  234 
troostite,  227 
tungsten,  247 
tungsten-chromium-vanadium 

steel,  249 
uses  of,  241 

uses  of  carbon  steels,  241 
weight  per  cubic  foot  of,  239 
welding  of,  238 
working  stresses  for,  240 
Steel  aUoys,  244 
aluminum,  247 
chrome,  247 
chromium-nickel,  248 
chromium -vanadium,  248 
classification  of,  244 
cobalt,  247 
copper,  248 
definitions  of,  244 
heat  treatment  of,  245 
manganese,  246 
molybdenum,  247 
nickel,  246 
nickel-vanadium,  249 
silicon,  247 
special,  243 
tungsten,  247 
tungsten-chromium-vanadium, 

249 


INDEX 


315 


Steel  alloys,  vanadium,  247 
Steel  belts,  274 
Steel  castings,  243 
annealing  of,  243 
definition  of,  243 
founding  of,  243 
minimum  requirements  for,  244 
properties  of,  244 
uses  of,  243 
Steel  manufacture, 

acid  Bessemer  process,  211 
acid  open-hearth  process,  215 
basic  Bessemer  process,  212 
basic  open-hearth  process,  216 
Bessemer  process,  209 

converter,  209 

mixer,  209 

plant  equipment,  209 
billet  heating  furnace,  220 
blowholes  in  ingots,  219 
casting  ingots,  219 
cementation  process,  208 
comparison   of   different   proc- 
esses, 219 

crucible  process,  208 
defects  in  ingots,  219 
duplex  process,  218 
electric  process,  217 
forging,  221 

gas-fired  pit  furnace,  220 
ingotism,  219 
ingot  molds,  219 
open-hearth  process,  213 

furnace  used,  213 

plant  equipment,  213 
piping  in  ingots,  219 
pressing,  221 
reheating  furnace,  220 

ingots,  220 
rolling,  220 

mills,  220 

segregation  in  ingots,  219 
soaking  pit,  219,  22C 
triplex  process,  218 
wire  drawing,  222 
Sterro-metal,  261 
Stone,  building,  89 
Stone  masonry,  119 


Stone  masonry,  backing,  123 

bond, 122 

classification,  120 

cleaning,  125 

cut  stone  or  ashlar  masonry,  121 

definitions,  119 

dressing,  122 

dry  masonry,  120 

general  rules  for  laying,  124 

in  general,  119 

mortar  for,  122 

pointing,  123 

properties  of,  125 

riprap,  120 

rubble  masonry,  120 

safe  loads,  126 

squared  stone  masonry,  120 

strength,  125 

waterproofing,  124 

wet  or  mortar  masonry,  120 
Structural       steel     for     buildings, 
standard  specifications,  291 

bend  tests,  292 

chemical  composition,  291 

chemical  properties,  291 

finish,  294 

inspection,  294 

ladle  analysis,  292 

manufacture,  291 

marking,  294 

number  of  tests,  294 

permissible  variation  in  thick- 
ness, 294 
variations  in  weight,  294 

physical  properties,  292 

rehearing,  296 

rejection,  296 

tension  tests,  292 

test  specimens,  293 
Surface  finish  of  concrete.  70 
Swedish  wrought  iron,  202 


Table  ware  alloy,  263 

Tentative  standards,  American 
Society  for  Testing 
Materials,  list  of,  297 


316 


INDEX 


Terne  plates,  253 
Terra  cotta,  111 
Timber,  135 

air  seasoning,  147 
artificial  seasoning,  147 
bamboo,  143 
beech,  143 
black  oak,  141 
spruce,  139 
walnut,  141 
broad-leaved      trees,       general 

characteristics  of,   140 
butternut,  141 
catalpa,  142 
chestnut,  142 
oak,  140 

classification  of,  144 
cleavability  of ,  155 
color  of  wood,  138 
common  rot,  151 
compressive  strength  of,  154 
conifers ;  general  characteristics, 

139 

Cyprus,  140 
decay,  149 
defects  in,  145 
dote,  146 
Douglas  fir,  139 
dry  rot,  150 
durability,  149 
endogenous    trees,    growth  of, 

137 

structure  of,  137 
eucalyptus,  142 
exogenous  trees,  growth  of,  135 

structure  of,    135 
factors  of  safety,  156 
flexibility  of,  155 
grain  of  wood,  138 
green  ash,  141 
gum,  142 
hard  maple,  141 
hardness  of,  156 
hemlock,  140 
hickory,  141 
influence  of  moisture   content, 

153 
injurious  insects,  151 


Timber,  inspection  of,  159 

kiln  drying,  147 

knots,  146 

lignum-vitse,  142 

live  oak,  141 

locust,  142 

logging,  143 

mahogany,  142 

marine  wood  borers,  151 

miscellaneous  properties,  156 

natural  seasoning,  147 

Norway  pine,  139 

odor  of  wood,  138 

Oregon  fir,  139 

palmetto,  143 

pitch  pockets,  146 

poplar,  142 

preparing  the,  143 

preservation,  160 

A.  C.  W.  process,  161 
Allardyce  process,  162 
Bethell  process,  161 
boiling  process,  161 
Boucheri's  process,  163 
Breant  process,  161 
brush  process,  160 
Burnett's  process,  162 
card  process,  163 
copper  sulphate,  163 
creo-resinate  process,  162 
creosote  process,  161 
Kreodone  process,  162 
Kyan's  process,  163 
Lowry  process,  162 
non-pressure  process,  160 
Payne's  process,  163 
pressure  process,  160 
Ruping  process,  162 
Seeley's  process,  161 
Thilmany's  process,  163 
vulcanizing  process,  163 
Wellhouse  process,  163 
zinc  chloride  pressure  process, 

162 

properties  of,  152,  1'57,  158 
red  ash,  141 
cedar,  140 
heart,  146 


INDEX 


317 


Timber,  red  ash,  oak,  141 

pine,  139 
redwood,  140 
rot,  146 

safe  working  loads,  156 
sawing,  144 
selection  of,  158 
shakes,  146 

shearing  strength  of,  155 
shrinkage,  148 
strength  in  general,  152 
tamarack,  140 
teak,  142 

tensile  strength  of,  154 
texture  of  wood,  138 
toughness,  156 
transverse  strength  of,  154 
trees  in  general,  135 
wane,  146 

water  seasoning,  147 
wet  rot,  151 
white  ash,  141 
cedar,  140 
elm,  141 
maple,  141 
oak,  140 
pine,  139 
spruce,  140 
walnut,  141 
white  wood,  142 
yellow  pine,  long  leaf,  139 

short  leaf,  139 
Tin,  257 

extraction  of,  257 
plating,  257 
properties  of,  257 
uses  of,  257 
Tobin  bronze,  261 
Trap,  90 
Trees,  135 
Troostite,  227 
Tungsten  steel,  247 

-chromium-vanadium  steel, 

249 
Turpentine,  267 


Vanadium  steel,  247 


Varnishes,  267,  268 
Voids,  coarse  aggregate,  53 

in  concrete,  53 

in  Portland  Cement  Mortar,  49 


W 


Wall  plaster,  19 

Waterproofing  brick  masonry,  130 

concrete,  72 

stone  masonry,  124 
Welding  of  steel,  238 

of  wrought  iron,  204 
White  lead,  267 
Wire  glass,  269 

rope,  273 
Wrought  iron,  197 

busheled  scrap,  197 

charcoal  iron,  197 

classification,  of  197 

composition  of,  201 

compressive  strength  of,  203 

constitution  of,  211 

Corrosion,  life  under,  250 

defects  in,  201 

definition,  197 

ductility  requirements,  205 

effect  of  annealing,  202 
of  coal  working,  202 

engine-bolt  iron,  197 

fracture  of,  203 

making  scrap,  201 

miscellaneous  properties,  205 

plate,  197 

properties  of,  201 

puddled  iron,  197 

refined  bar  iron,  197 

shearing  strength,  203 

staybolt  iron,  197 

Swedish,  202 

tensile  strength,  202 
requirements,  205 

transverse  strength,  203 

uses  of,  206 

welding  of,  204 

working  stresses  for,  205 
Wrought  iron  manufacture,  198 

dry-puddling  process,  200 


318 


INDEX 


Wrought          iron         manufacture, 

reheating  muck  bars,  201 
rerolling  muck  bars,  201 
rolling  muck  bars,  201 
shingling  puddle  balls,  200 
squeezing  puddle  balls,   200 
treatment  of  puddle  balls,  200 
wet-puddling  process,    198 
boiling  stage,    199,    200 
cleaning  stage,  199 
furnace  operation,  199 
furnace  used,  198 


Wrought     iron    manufacture,     wet 
pudding    process,  mate- 
rials for,  198 
melting  down  stage,  199 

Z 

Zinc,  256 

extraction  of,  256 

properties  of,  256 

uses  of,  257 
Zinc  white,  267 


UBRAEY 


Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 


DEC 


REC'D  LD 

JUN7    1963 


NOV3019658 
REC'D 

HWlfa'65-lDPI 

LOAN  DEPT, 


LD  21-100«v-9,'47(A5702816)476 


4888-J9 


kLBRARY 


